Lake Koocanusa is a transborder reservoir in British Columbia (Canada) and Lincoln County, Montana (United States). It was formed in 1972 by the damming of the Kootenai River by Libby Dam, a joint project between the two countries. The reservoir reaches a depth of 370 feet (112.78 meters) and covers approximately 26,720 acres (108 km2). Libby Dam is a multi-purpose project, ensuring flood reduction, hydropower, and recreational activities. The construction was a huge undertaking, at some point employing 2,000 workers, and resulted in an incredibly strong dam, created by 47 monolithic sections, each able to stand on its own.
The reservoir is large but with limited bank access, so it is recommended to bring a boat. Montana’s longest and highest bridge, Koocanusa Bridge, provides access across the northern end of the reservoir. Lake Koocanusa belongs to the western district, where the general fishing season in rivers and streams is open from the third Saturday in May through to November 30th, but the lakes and reservoirs are open all year. A valid Montana fishing license is required, and the use of live bait is entirely prohibited.
It is important to note for all interested in activities on and around the water, that the adjacent Kootenai River holds an aquatic invasive species (AIS) warning for curlyleaf pondweed (Potamogeton crispus). It’s therefore crucial to remember to clean, drain, and dry all gear and transport devices to avoid spreading this species. The curlyleaf pondweed was most likely unintentionally introduced when stocking fish but has since spread and can form dense mats that both outcompete native species and hinder recreational activities.
Fish Species in Lake Koocanusa
1) Brook trout (Salvelinus fontinalis)
The brook trout is a member of the Salmonidae (salmonids) family characterized by small scales, and most obviously the adipose fin located between the dorsal and tail fin. This species can be distinguished from other salmonids by their dark green marbling on the dorsal side and the red spots marked by a blue outline on their flanks. They have a green to brown base color that fades towards a lighter belly, but their color can vary, especially in the spawning season, when the lower sides and fins become red.
The brook trout was introduced to Montana in 1889 from eastern North America. Historically, it was a popular species to stock, however, this practice is less common today. However, the species is still cultured for food and stocking in some areas, and it is widely used as an animal for experiments. They prefer cool, well-oxygenated waters, where they feed on crustaceans and aquatic invertebrates. However, they are known to be opportunistic predators also feeding on mollusks, amphibians, and even small mammals.
The brook trout can be caught at Lake Koocunusa with a daily possession limit of 20 fish. They do not count towards the daily combined trout limit.
2) Bull trout (Salvelinus confluentus)
The bull trout belongs to the Salmonidae (salmonids) family. Interestingly, the first part of the Latin name, ‘salvelinus’, is the old word for char and means ‘little salmon’, while the English common name includes ‘trout’. This is curious because char and trout are two distinct genera that can be visually distinguished by their color. Trout have dark spots on a lightly colored background, as one might be familiar with from the rainbow trout. Char have light spots on a dark background, effectively marking the bull trout as a char. They can be further recognized by the lack of spots on the dorsal fin and a slightly forked tail.
The bull trout is native to Montana, where the population numbers have followed a slow downward trend. They are sensitive to changes in their spawning environment, as too much sediment can suffocate the eggs. At the same time, they mature late (around the age of four or five), which makes them sensitive to overharvest. The species is listed on the IUCN Red List of Threatened Species as ‘Vulnerable’ under the criteria A2e since 1996. Therefore, any caught individuals must be released upon identification, as federal rules prohibit targeting of the species unless special authorization has been given.
3) Burbot (Lota lota)
The burbot is a member of the Lotidae (hakes and burbots) family, which falls under the Gadiformes (cod) order. It is the only Lotidae member that inhabits freshwater, therefore, it is sometimes referred to as the freshwater cod. The species sport a dark-mottled yellow to brown coat. The flanks have no visible scales, and the pelvic fins are pale. It can be distinguished from other freshwater species by its long second dorsal fin and single central chin barbel. The barbel is taste-sensitive and helps the burbot locate its food. Younger individuals feed predominately on aquatic invertebrates, whereas older individuals are piscivores.
The burbot can be caught in Lake Koocanusa, but you are restricted to 2 individuals daily and in possession. This is due to their irregular occurrence, as they can be rare in some parts of their range. In the state of Montana, the population below the Libby Dam is the only population in which a steady decline has been recorded. They are usually found in sizeable streams and in cold and deep reservoirs, where they peak in activity during the night. They spawn in winter beneath the ice and are popular among ice fishers.
4) Kokanee salmon (Oncorhynchus nerka)
The kokanee salmon belongs to the Salmonidae (salmonids) family and can be described as a landlocked version of the Pacific sockeye salmon. They were originally introduced to Montana in 1914 and are now widespread in the western half of the state. They are predominantly distinguished from other salmonids by their long, serrated, and closely-spaced gill rakers on the first arch.
Before spawning, they don a silver coat with a green or blue dorsal side with no definite spots, although some individuals may have a few. At spawning, which typically happens around four years of age, the color of the male changes to a deep red with a green head, while the female’s colors tend to be duller. The adult fish die following spawning.
The kokanee salmon is one of the most abundant fish species in the Koocanusa Lake. They serve as a key species in the food web. They predominately consume zooplankton of the Daphnia spp. and Diptera spp. genera, where the latter is more dominant in spring. The general restrictions when fishing for kokanee in the western district are 20 daily and 40 in possession, but these numbers have been extended to 50 daily and 100 in possession for the Koocanusa Reservoir.
5) Largemouth bass (Micropterus salmoides)
The largemouth bass is the largest member of the Centrarchidae (sunfish) family. They can reach sizes beyond 20 lbs (9 kilograms), however, the largest specimen caught in Montana weighed a mere 9.58 lbs and measured 22.5 inches (4.35 kilograms, 57.15 centimeters). They have a deep olive-green base color, a lighter-colored belly, and a dark line running from the operculum to the base of the tail fin. They can be distinguished from similar species by their large mouth which extends at least to the rear edge of the eyes. They are opportunistic hunters preying predominantly on fish, crayfish, and amphibians as adults, while juvenile largemouth bass feed on crustaceans, aquatic insects, and small fish.
The largemouth bass has been widely introduced across the United States and, despite the warmer waters of their native distribution, they can survive in Lake Koocanusa. However, they are often subject to winterkill and must be restocked, which is partly why they are under a fishing restriction of 5 daily and in possession, with only 1 individual larger than 12 inches (30.48 centimeters), however from the third Saturday in May to June 30th, the daily and possession limit is reduced to one individual, which must be bigger than 22 inches (55.88 centimeters).
6) Largescale sucker (Catostomus macrocheilus)
The largescale sucker is a member of the Catastomidae (suckers) family. They sport an olive dorsal side which abruptly becomes yellowish on the belly. The body is elongated, and the snout is rounded with a downturned mouth. The species is characterized by 13 – 15 rays on the dorsal fin.
The largescale sucker is abundant in most freshwater systems west of the Rocky Mountains; however, they have decreased in abundance below the Libby Dam. This is likely due to low water temperatures, as the species is not a popular game fish. They are common in relatively shallow parts of the river or reservoir and are opportunistic omnivore bottom feeders. Here they predominantly feed on algal periphyton, aquatic invertebrate larvae, crustaceans, and snails.
This species spawns in late spring, and the fry grow rapidly on a diet of plankton in the first year. The fry often form mixed schools with juvenile Cyprinids. The males mature slightly earlier than the females, which usually grow larger than their male counterparts. Therefore, the largest individuals found are likely to be female. However, for sexually mature individuals, the males can be identified by an elongated lower caudal fin lope and longer anal fins.
7) Longnose dace (Rhinichthys cataractae)
The longnose dace is a member of the Leuciscidae (minnows) family. While ‘dace’ is a broadly used term to describe any of the North American cyprinid fishes, the longnose dace is a moderately sized minnow with an elongated body covered in a ‘salt and pepper’ sprinkle. The breeding males sport reddish fins and develop a redder chin. Their ‘nose’ extends beyond the upper lip resulting in a strongly downturned mouth. This comes in handy when they feed on aquatic invertebrates and algae, which they nipple off rocks.
The longnose dace is an abundant species in many North American freshwater systems. Therefore, the species lends itself well to investigating the aversive effects of aquatic contaminants. In Alberta, a study set out to determine the physiological responses and consequences of compounds known as endocrine-disrupting compounds, which can interfere with the natural hormone levels and processes. At multiple sites in the Oldman River, a female-biased sex ratio was observed, meaning that there were more females than males. This contrasted with an unimpacted reference site, where the sex ratio was more even. Concurrently, intersex fish, meaning individuals with both male and female reproductive organs, were found at multiple sites. Since intersex is an unusual state for the longnose dace, it was concluded that the species was indeed affected by the hormone-disrupting compounds.
8) Longnose sucker (Catostomus catostomus)
The longnose sucker is a member of the Catastomidae (suckers) family and has the greatest state-wide distribution out of all Catostomidae members (Montana). They have an olive-brown to almost black dorsal side, which pales towards a white belly. The colors of the breeding males intensify during spawning migrations in spring, where they sport bright red highlights and an almost black dorsal side.
The longnose sucker was not common in the Kootenai River before impoundment; however, the preferred habitat of this bottom-dwelling sucker is cold, clear, and deep water, which, by the formation of the Libby Dam, was expanded, resulting in a positive effect on the population.
The longnose sucker was most recently assessed by the IUCN Red List of Threatened Species in 2020, where it was categorized as ‘Least Concern’. The evaluation is based on the species being widespread across its native habitat, despite localized threats. These include certain populations subjected to the destruction of river ecosystems for the development of gold mines, and the population in Lake Michigan, which suffers from deteriorating water quality and competition from non-native species. Regardless, the global population is stable and therefore the species in general is of relatively low conservation concern.
9) Mountain whitefish (Prosopium williamsoni)
The mountain whitefish, also known as the Rocky Mountain helt, is a member of the Salmonidae (salmonids) family characterized by an adipose fin between the dorsal fin and the tail fin. This species has a slender, elongated body, which is comparatively more laterally compressed than the closely related round whitefish. They have a pointed snout, which hangs over the mouth, and a silvery coat, which dorsally may have pigmented borders, giving a darker hue. The fins are often more colorful, with adults sporting yellowish-brown pelvic and pectoral fins.
The mountain whitefish is familiar to most in Montana, as it is a common species in the state. They often assemble in the fall on spawning runs. Afterward, their eggs adhere to gravel bars in tributary streams. Some anglers consider the mountain whitefish a competitor to the often more popular trout, however, their diets differ significantly, and species such as the brook trout consume mountain whitefish fry. The mouth of the mountain whitefish is small and round and is adapted to consume mostly benthic invertebrates.
The mountain whitefish can be caught by the interested angler following a daily limit of 20 individuals and a possession limit of 40.
10) Northern pike (Esox lucius)
The northern pike is a member of the Esocidae (pikes) family, whose scientific name means “pike pike” in Greek and Latin. This charismatic predator has an elongated, cylindrical body draped in an olive coat with light oval markings ordered in vertical rows. The belly is white, and the fins sometimes have an orange tone.
The northern pike occurs predominantly in clear lakes with aquatic vegetation, quiet pools, or rivers. They are hide-and-strike piscivores who hold individual territories. Due to their preferred hunting technique, any attempt at cultivating them has failed, as they refuse to accept artificial food.
In Wisconsin and Minnesota, a unique variant of northern pike exists. This pike is entirely silver, sometimes gold-speckled, and not otherwise marked like the wild-type pike. This unique color arises from a rare genetic variation, that occasionally surfaces throughout the global population. Due to its coloration, it is often called the silver muskellunge, although silver pike would be more fitting.
The northern pike is a popular game fish and has been introduced to Lake Koocanusa. For anyone interested in catching this majestic species, a daily possession limit of 15 individuals must be respected.
11) Northern pikeminnow (Ptychocheilus oregonensis)
The northern pikeminnow was formerly known as the ‘northern squawfish’ and is a member of the Leuciscidae (minnows) family. Minnows are characterized by having only one dorsal fin and their pelvic fins are located far down the body. They do not have teeth in their mouth but on a bone in their throat. The northern pikeminnows are silvery with a dark green dorsal side. The breeding males develop yellow to orange pectoral and pelvic fins.
The northern pikeminnow spawn in early spring, where males congregate around spawning sites. Females arrive later to the sites and will often be courted by multiple males. Both males and females might spawn/milt multiple times in a breeding season.
The northern pikeminnow was most recently assessed by the IUCN Red List of Threatened Species in 2012, where it was listed as ‘Least Concern’. This assessment was based on a large, stable global population, which over the past 10 years has shown no obvious signs of decline. The species might face local threats, but no general threat has been identified. The species tends to be content in still and slow-moving waters. There is often a spatial distribution related to age in lakes, where older individuals are found further from shore than younger fish.
12) Peamouth chub (Mylocheilus caurinus)
The peamouth chub or simply peamouth is a member of the Leuciscidae (minnows) family. They have a slim silvery body with a single dorsal fin and abdominally placed pelvic fin, characteristic of the family. They have a dark dorsal side and two dark stripes running down the side of the body. They have a small mouth, which most likely is the characteristic their name refers to. In the corners of the mouth, a little barbel can be seen. The surrounding skin is frequently reddish, and breeding males additionally sport a red stripe along their flanks.
Compared to other freshwater species, the peamouth is somewhat tolerant to salt water. Longstanding research on their salinity tolerance showed that they could survive four to five days at around 15 parts per thousand. The species, whose native range predominantly covers Montana and Southwest Canada, can therefore be found on certain offshore islands. While the Strait of Georgia usually works as a barrier to freshwater fish, in periods of very high levels of run-off from the Fraser River, a low-salinity corridor opens in the strait. It is believed that it is during these periods that the Peamouth colonizes the offshore islands.
13) Pumpkinseed (Lepomis gibbosus)
The pumpkinseed is a deep-bodied, laterally-compressed member of the Centrarchidae (sunfish) family. The shape of the body resembles that of the seed the fish has been named after. They have a dark brown to olive coat that lightens towards an orange-red breast and belly. Both their flanks and back sport colorful spots and their sides are interrupted by seven to ten vertical bands. These tend to be more obscure in males than females, especially compared to the prominent bands of breeding females. The operculum flap is black with a thin, light-colored margin and a half-moon cherry spot on the posterior side.
The pumpkinseed is not native to Lake Koocanusa, but whether it was intentionally introduced, a result of several accidental releases, or whether the species has established itself since it was introduced to the Columbia River system in the early 1900s continues to be a mystery. The first registered specimen was collected from the lake in 1974 and has since established a stable breeding population. The species is sometimes considered a threat to native fish species, as this highly ecologically tolerant, opportunistic feeder has the potential to outcompete native species. However, these are the same properties that formerly led to the use of pumpkinseed fish as pest control.
14) Rainbow trout (Oncorhynchus mykiss)
The charismatic rainbow trout belongs to the Salmonidae (salmonids) family. They have a laterally compressed, streamlined body. The species is known for its beautiful coloration, with blue-green sides and dorsal sides, silvery sides, and a broad rosy stripe. The flanks, fins, and head are covered in dark circular spots.
The rainbow trout found in Lake Koocanusa originate from hatcheries, where clipping is a common practice. Here, the adipose fin, which is located between the dorsal and tail fins, is removed for later identification. This makes it possible to identify salmon of hatchery vs wild origin. The hatchery strain is sterile. Any individual less than 22 inches (55.88 centimeters) with a clipped adipose fin must be released. The rainbow trout counts toward the combined trout tally in the western district, which has a 5 daily and 10 in-possession limit for lakes and reservoirs with only one individual over 22 inches (55.88 centimeters) permitted.
The Montana state record rainbow trout was caught in the Kootenai River off of David Thompson Bridge in 1997 by Jack G. Housel, Jr. and this river monster measured 38.62 inches and weighed 33.1 lbs (98 centimeters, 15 kilograms)!
15) Redside shiner (Richardsonius balteatus)
The redside shiner is a member of the Leuciscidae (minnows) family. They have a laterally compressed, somewhat deep body with a striking black line running from the gill cover to the start of the tail highlighted by a narrow light stripe above. The dorsal side of the fish is dark olive and the belly silvery. During the breeding season, the males develop a prominent red and yellow side, which has most likely given the species its common name.
The redside shiner overwinters in undercut banks, near fallen trees, and in backwaters offering cover and refuge from the current. During spring, the adults move to faster waters to spawn, whereas the younger individuals stick to the protected habitats. Large, deep pools are important for their occurrence, but they are usually considered an abundant and widespread species. They provide an important food source for the salmonids in Lake Koocanusa.
Previously, the redside shiner and its sister species, the Lahontan redside, were considered subspecies of the redside shiner. The main difference between the two species is the number of anal rays, which is almost double in the redside shiner (10 – 24 anal rays) compared to the Lahontan redside (8 – 9 anal rays).
16) Westslope cutthroat trout (Oncorhynchus clarkii lewisi)
The westslope cutthroat trout belongs to the Salmonidae (salmonids) family. It is the official state fish of Montana, together with the other subspecies of cutthroat trout. These two species are the only native subspecies of cutthroat in the state. The cutthroats, or “cutties”, get their unique name from the red mark below their chin. The westslope can be difficult to distinguish from other cutthroat species but are characterized by their silvery green color, a multitude of small spots by the tail, but none on the pectoral fins, and an average size between 6 and 16 inches (15.24 to 40.64 centimeters).
Interestingly, the cutthroat trout can hybridize with the rainbow trout, despite not being the closest relative within the Oncorhynchus genus. However, this relationship is still being discussed, as morphological and mitochondrial DNA data disagree about the phylogenetic relationship.
The westslope cutthroat trout can be caught in the western district with daily and possession limits of 3 individuals in lakes and reservoirs, with no size limit. However, it should be noted that the species has been given a state status of ‘S2’; this means that the species is at risk due to a very limited or potentially declining population, habitat, and/or range, which makes the species vulnerable.
17) Yellow perch (Perca flavescens)
The yellow perch is a member of the Percidae (perch) family with an elongated, oval body. They have a yellow-green coat that darkens toward the dorsal side and lightens toward the belly. The flanks sport six to seven dark vertical bands and their eyes are strikingly yellow-green.
The yellow perch is a non-obligatory plant spawner. They do not construct nests and the eggs and young are left unguarded. The egg strands are distinctive as the large gelatinous matrix is accordion folded and can be found draped over aquatic vegetation or submerged branches. During the first two years, the juveniles grow rapidly. They are generalist feeders and can utilize a great variety of prey, from aquatic insects to smaller fish.
The yellow perch is a highly adaptable species that occurs in many different types of habitats. This has also led to a series of introductions of this species to non-native waters. Before impoundment, the yellow perch was not present in the Kootenai River, but it now resides there. Some consider the yellow perch a problematic species since it can outcompete salmonids, as they rely on a similar food source. However, this effect is somewhat negated in large water bodies.
