The largest lake in the world’s first national park, Yellowstone Lake holds the title of the largest high-altitude lake in North America. Located in Wyoming at the southwest corner of Yellowstone, the lake is just 20 miles east of Old Faithful. The Continental Divide National Scenic Trail curves along the western edge of the lake, with the Absaroka Mountain Range to the east. Yellowstone Lake drains into the Yellowstone River, flowing northward into the Grand Canyon of the Yellowstone.
A bit further to the south in Bridger-Teton National Forest lies Two Ocean Pass, notable for its two creeks where one ultimately flows into the Pacific Ocean and another flows into the Atlantic ocean. This pass is thought to have provided the route by which cutthroat trout originally colonized Yellowstone Lake more than 10,000 years ago — but may also explain how non-native lake trout arrived in the more recent past.
Despite 110 miles of shoreline, due to the cold year-round temperatures, swimming in this lake is not recommended (for humans at least!). However, a variety of water activities including boating and fishing remain popular options for exploring the aquatic environments of Yellowstone.
Located within the Native Trout Conservation Area of the park, the fishing regulations of Yellowstone Lake require that all native fish be released but there is no possession limit on non-native fish. Though the park is home to 11 native and 5 non-native fish species, some fish are only found in certain waterways. The following article describes several common fish found in Yellowstone Lake or Yellowstone River.
Native Fish Species in Yellowstone Lake
1) Cutthroat trout (Oncorhynchus clarkii)
Members of the Pacific trout genus, two subspecies of cutthroat trout — the Yellowstone cutthroat trout (O. c. bouvierii) and the westslope cutthroat trout (O. c. lewisi) — can be found in Yellowstone Lake. Both species primarily consume aquatic insects, such as mayflies, caddisflies, and stoneflies, as well as smaller fish, frogs, algae, and other small terrestrial animals that may fall into the water.
Like many cutthroat varieties, these fish display a distinct red slash along their jawline, leading to the popular fishing adage “if it has a red slash, put it back”. They can also be distinguished from other fish based on the presence of only a few spots on top of their head and dark ovals on the sides — called parr marks — that are retained even by adult fish.
Yellowstone cutthroat trout are the most widespread native trout subspecies in Yellowstone overall, with Yellowstone Lake and Yellowstone River providing the largest genetically-pure population of this fish in the world. Westslope cutthroat trout (the state fish of Montana) were historically the most common subspecies of cutthroat trout but were nearly eliminated from Yellowstone by the 1930s due to competition with non-native trout and interbreeding with other species (including both rainbow trout and Yellowstone cutthroat trout). Though similar in appearance to westslope cutthroat trout, Yellowstone cutthroat trout can be distinguished by their lighter, less greenish color and presence of larger round spots that become denser near its tail.
Both subspecies of cutthroat trout have been threatened by habitat destruction, overfishing, and a parasite that causes whirling disease. Non-native fish also pose serious threats to native cutthroat via competition for resources, hybridization, and predation by lake trout.
Since cutthroat trout live part of their lives near the water surface and spawn in streams and tributaries, they are frequently captured prey items for iconic Yellowstone wildlife such as grizzly and black bears, eagles, ospreys, river otters, and mink. They are considered a “keystone species” — that is, a type of animal with a disproportionately large effect on its ecosystem.
2) Mountain whitefish (Prosopium williamsoni)
The mountain whitefish can be found in Yellowstone River, as well as in the Snake and Lewis Rivers. Primarily a stream-dwelling species, they tend to be abundant in clear, cold water. These fish belong to the family Salmonidae, which also includes trout and salmon.
Typically a bottom-feeder, mountain whitefish are small and silvery. They have a toothless mouth, used to consume the larvae of aquatic insects and small crustaceans. Cylindrical in shape, the mountain whitefish ranges from 10 to 16 inches in length, although record sizes can exceed five pounds.
Generally considered widespread and common throughout much of the northwestern United States and parts of southwestern Canada, like many other fishes they are threatened by whirling disease. The causative agent of whirling disease is the parasite Myxobolus cerebralis, which causes skeletal and neurological damage to juvenile fish, ultimately leading to swimming in a “whirling” motion that makes feeding difficult. Predation and drought have also been documented as potential threats to mountain whitefish populations. As these fish are highly sensitive to pollution, they can serve as important environmental sentinels of water quality.
3) Minnows (Cyprinidae)
Four species of small minnows can be found in Yellowstone. The longnose dace (Rhinichthys cataractae), which is the most widely distributed minnow in North America, has a sucker-like mouth that it uses to bottom-feed on the larvae of blackflies, midges, and mayflies, though they are highly opportunistic and will eat many items ranging from algae to fish scales.
The speckled dace (Rhinichthys osculus) displays a similar habitat preference and appearance, though slightly smaller and lacking an elongated snout. True to its name, the redside shiner (Richardsonius balteatus) can be distinguished from other minnows by its red side patches, with breeding males, in particular, displaying bright red and yellow colors.
All 3 minnow species occasionally hybridize with each other. Though not considered game fish, these minnows are sometimes used as bait for larger fish (although baiting in Yellowstone is not allowed) and provide an important food source for larger fish species.
4) Utah chub (Gila atraria)
A member of the same family as minnows, but larger in size, the Utah chub can exceed a pound in weight. These fish are variable in color, and can range from olive-brown to nearly black, usually with a silvery or whitish underside and brassy or silver sides.
Originally found in the nearby Heart, Lewis, and Shoshone Lakes, this fish was probably introduced to Yellowstone Lake in the 1950s. Their native range includes western Utah, south and eastern Idaho, and parts of western Wyoming including areas within Yellowstone. These fish are highly omnivorous, feeding on zooplankton as well as small aquatic invertebrates and plants. Like the smaller minnows, Utah chub also serve as prey items for other fish including cutthroat trout.
5) Suckers (Catostomidae)
Suckers got their name not because they planned poorly for their Yellowstone visit, but rather due to their specially-adapted mouths that they use to scrape away detritus and algae from rocks, while occasionally consuming aquatic plants and small invertebrates! The longnose sucker (Catostomus catostomus) is identifiable by its cleft lower lip, and can be found throughout North America as well as in eastern Siberia. It is particularly well-adapted to cold water and is the only suckerfish also found in Alaska.
More common especially at higher altitudes, the mountain sucker (C. platyrhynchus) displays more herbivorous habits. Similar to the olive-toned longnose sucker in appearance, the mountain sucker can be distinguished by its shorter snout and smaller size.
Finally, the Utah sucker (C. ardens) is typically larger, darker, and more elongated than other Yellowstone suckers, while also tolerating warmer waters. Though not commonly sought after as game fish, suckers are important prey items for Yellowstone wildlife, especially bears, river otters, and birds. Contrary to popular myths, most species of suckers require clean water, do not consume large amounts of trout eggs, and function as important members of freshwater ecosystems. Within Yellowstone Lake, declines in suckers have been documented, which may be attributable to predation by lake trout during the winter.
6) Mottled sculpin (Cottus bairdii)
Found only in parts of Yellowstone River below the Lower Falls, but not in Yellowstone Lake, the mottled sculpin generally resides in shallow, sometimes fast-moving water where they feed mostly on benthic (bottom-dwelling) insects or other invertebrates.
Though easily distinguished from other fish species by their large mouths and fan-like fins, the “mottling” or speckled pattern of this sculpin species functions as camouflage against their rocky habitats. To avoid being eaten by predators such as snakes, mergansers, and other fish, mottled sculpin can modify their colors to blend in with their surroundings — like a more subtle version of a chameleon. Mottled sculpin males also display courtship behaviors, excavate nests, and provide parental care for their eggs.
Non-Native Fish Species in Yellowstone Lake
1) Lake trout (Salvelinus namaycush)
First documented in Yellowstone Lake in 1994, lake trout are a serious threat to Yellowstone’s native fish, especially cutthroat trout. Prized as sport fish for their massive size, lake trout were intentionally stocked in some areas of the park, such as Lewis Lake and Shoshone Lake, in the 1890s. How they arrived in Yellowstone Lake and whether humans were involved, however, remains hotly debated.
Not only are lake trout voracious predators of smaller fish, but their behavior and preferred habitat also make them more difficult for predators to capture. Typically, lake trout reside in deep water and spawn within the lake, making them more difficult for predators to capture.
Since their invasion of Yellowstone Lake, the introduction of lake trout has led to drastic declines in cutthroat trout populations and corresponding declines in predators including bears, otters, and birds, that rely on cutthroat trout for food. Due to less availability of fish, grizzly bears shifted their diets to include other prey such as elk calves.
The loss of cutthroat trout may also be related to an increase in the size of zooplankton (common prey of cutthroat trout) and a corresponding increase in water clarity. This collapse of the Yellowstone Lake food web — also called a trophic cascade — sparked efforts to reduce lake trout and restore the native cutthroat trout.
After several years of massive conservation actions including encouraging sport fishing for lake trout, mass removals of lake trout, and depositing pellets that kill lake trout embryos, lake trout populations in Yellowstone Lake have decreased and cutthroat trout populations have begun to slowly recover.
2) Brown trout (Salmo trutta)
Not only are brown trout non-native to Yellowstone, but they were also originally introduced from Europe and are not native to the US at all! Though not found in Yellowstone Lake, they are common in the Yellowstone River and several other large rivers in the park. A popular game fish, they are widespread in the United States and are stocked by many states.
Brown trout can be distinguished from other trout by the presence of a pale “halo” around their black spots. Though they primarily feed on aquatic invertebrates, their diets occasionally include terrestrial insects or other fish. Through predation and competition, brown trout have been associated with reduced native fish populations in some areas.
3) Lake chub (Couesius plumbeus)
A member of the family Leuciscidae, also known as the true minnows, the lake chub is a small fish that is rarely more than six inches in length. These non-native fish were likely introduced by humans as baitfish. They are considered uncommon in Yellowstone Lake, but are more frequent in other areas including some creeks in the northeast corner of the park.
Their scientific name plumbeus, meaning “made of lead” refers to the silvery color of their sides. These fish have a small, toothless mouth, and they primarily feed on zooplankton as well as algae and aquatic insect larvae. During breeding, male lake chubs develop red patches near their mouth and at the bases of their fins.
Arctic grayling, rainbow trout, and brook trout are also found elsewhere in Yellowstone National Park but not in Yellowstone Lake or Yellowstone River specifically.
