What kind of fish are in Yellowstone Lake?

Yellowstone Lake, located in the heart of Yellowstone National Park, is not only the largest high-elevation lake in North America but also an ecologically complex aquatic system. Its fish population reflects the natural history, human impact, and conservation efforts that have shaped the Yellowstone region. 

The lake contains a mix of native and non-native fish species, with a strong emphasis today on protecting and restoring native populations, particularly the Yellowstone cutthroat trout. Below is a detailed overview of the key fish species associated with Yellowstone Lake.

1. Yellowstone Cutthroat Trout (Oncorhynchus clarkii bouvieri):

This native trout species is historically significant and is considered the native top predator in Yellowstone Lake. Yellowstone cutthroat trout are known for their golden-yellow coloring and distinctive red slash marks beneath their lower jaws. They are vital to the lake's ecosystem, serving as an essential food source for bears, ospreys, bald eagles, otters, and other wildlife. These fish spawn in tributary streams such as Clear Creek, and their lifecycle connects the lake to surrounding habitats. Due to their ecological importance, extensive efforts are made to protect and restore the population of Yellowstone cutthroat trout in the lake, which has declined sharply in recent decades due to predation by invasive species.

2. Lake Trout (Salvelinus namaycush):

Lake trout are not native to Yellowstone Lake. They were illegally introduced into the lake in the 1980s, likely transferred from nearby waters where they had been stocked for sport fishing. Lake trout live in the deep, cold waters of the lake and prey heavily on native Yellowstone cutthroat trout, significantly reducing their numbers. Unlike cutthroat trout, lake trout do not spawn in streams, making them unavailable to terrestrial predators, and their presence has disrupted the entire food web. Their population has grown so much that aggressive management strategies—including netting and killing—have been implemented by the National Park Service to control their numbers and protect native species.

3. Arctic Grayling (Thymallus arcticus):

Once present in Yellowstone Lake, the Arctic grayling is now considered extirpated (locally extinct) from the lake. This elegant, sail-finned fish was native to the upper Yellowstone River basin but disappeared due to habitat alteration, competition from non-native fish, and possible changes in water chemistry. Arctic grayling still exist in other parts of Yellowstone National Park, such as Grebe and Wolf Lakes, and restoration efforts are being explored to reintroduce this native species to suitable habitats within the park.

4. Mountain Whitefish (Prosopium williamsoni):

These native whitefish are part of the salmon family and can be found in several rivers and lakes in the Yellowstone ecosystem, including Yellowstone Lake. Mountain whitefish are generally found in cold, clear waters and feed on aquatic insects and small invertebrates. They are often overlooked in the fishing community but play a significant ecological role by contributing to the diet of larger predators and maintaining balance in aquatic food webs.

5. Longnose Sucker (Catostomus catostomus):

This is another native species that inhabits Yellowstone Lake. Longnose suckers are bottom-dwelling fish that feed on detritus, algae, and invertebrates. Though not as charismatic as trout, they are an important part of the lake’s ecology. They help recycle nutrients and provide food for predatory birds and mammals. Longnose suckers are more tolerant of environmental changes and continue to persist despite the challenges that have affected other native fish.

Other Introduced Species in Nearby Waters (Not Found in the Lake Itself)

While not present in Yellowstone Lake, other species like rainbow trout, brook trout, and brown trout have been introduced into nearby park waters for sport fishing and have caused problems through hybridization or competition.

In some cases, hybridization between Yellowstone cutthroat and rainbow trout (Oncorhynchus mykiss) has led to the creation of hybrid fish known as cutbows, threatening genetic purity.