Fish in Flathead Lake

Fish in Flathead Lake: A Species-by-Species Guide

Flathead Lake in northwest Montana is not only the largest natural freshwater lake in the western United States—it is also a rich, dynamic ecosystem that supports a diverse community of fish species. From deep-dwelling giants to shoreline favorites, the lake offers something for every kind of angler and nature lover. Below is a detailed guide to the primary fish species found in Flathead Lake.

1. Lake Trout (Mackinaw)

Lake trout are the most abundant and well-known game fish in Flathead Lake. Introduced in the early 1900s, these powerful predators thrive in the lake’s deep, cold waters. Lake trout can reach impressive sizes, often weighing 10 to 30 pounds, and some have been recorded at over 40 pounds. They are typically found at depths between 100 and 200 feet during summer but move closer to the surface in spring and fall. Anglers use trolling and jigging techniques to catch them, especially during events like Mack Days, which help manage their population.

2. Bull Trout

Bull trout are native to the Flathead Lake system and are considered a threatened species under the Endangered Species Act. They resemble lake trout but have smaller heads and more pronounced pale spots. Unlike lake trout, bull trout are strictly protected in the lake and must be released immediately if caught. They are a vital part of the native ecosystem, and conservation efforts focus on restoring their populations, which have declined due to competition with non-native species.

3. Westslope Cutthroat Trout

Another native species, the westslope cutthroat trout, is Montana’s state fish and an important symbol of the region’s natural heritage. These trout are generally found in the cooler tributaries and streams flowing into Flathead Lake, but some also reside in the lake itself. Known for the distinctive red or orange slash under their jaws, cutthroat trout are prized by fly fishers and are a key species in ongoing conservation efforts.

4. Lake Whitefish

Lake whitefish are a deep-bodied, silver-scaled fish that were introduced to Flathead Lake in the early 1900s. They are an important part of the lake’s fishery and are commonly caught during the fall, when they spawn in shallow water. Whitefish are bottom-feeders, often found in schools, and are typically targeted using jigs. While not as aggressively pursued as lake trout, they provide excellent table fare and contribute to the lake’s food web.

5. Yellow Perch

Yellow perch are small, colorful fish that thrive in the warmer, shallower bays around the lake. They are especially popular with beginner anglers and families because they are relatively easy to catch from the shore. Perch travel in schools and bite readily on small hooks and live bait. Though not a native species, they have established a stable population and are a favorite for panfishing in summer.

6. Northern Pike

Northern pike, known for their sharp teeth and aggressive behavior, are found in some of the weedy, shallower areas of Flathead Lake. They are not native and were likely introduced accidentally or through nearby connected waters. These ambush predators are formidable fighters and can reach lengths over 30 inches. While their numbers are relatively limited in the main lake, they offer an exciting challenge for anglers looking for something different.

7. Smallmouth Bass

Smallmouth bass are found primarily in the rocky areas and river mouths along the shoreline, especially on the eastern side of the lake. They are not native but have adapted well to the lake’s conditions. These hard-fighting fish are popular with sport anglers and are known for their acrobatic leaps when hooked. Summer is the best season for targeting smallmouth bass, especially in the early morning and late evening hours.

8. Largemouth Bass

Less common than smallmouth, largemouth bass prefer warmer, vegetated areas around the lake’s southern bays and river inlets. They are usually found in lower densities but can be caught near submerged logs, docks, and aquatic plants. Largemouth bass fishing is best in late spring and summer, and they respond well to topwater lures and soft plastics.

9. Rainbow Trout

Rainbow trout are occasionally found in Flathead Lake but are more common in its tributaries and nearby rivers. They are stocked in some connected waters and can occasionally make their way into the main lake. These fish are known for their pinkish lateral stripe and lively fight. Though not a primary target species in Flathead Lake itself, they add to the diversity of the watershed.

10. Kokanee Salmon (Formerly Present)

Kokanee salmon, the landlocked form of sockeye salmon, were once abundant in Flathead Lake. They supported a popular sport fishery through the mid-20th century. However, due to competition from introduced lake trout and mysis shrimp, kokanee populations declined sharply in the 1980s and were eventually extirpated from the lake. Their disappearance remains a notable case study in how non-native species can dramatically alter native fish communities.

Fish in Flathead Lake: Quick Summary

Species	Native/Introduced	Habitat in Lake	Fishing Notes
Lake Trout	Introduced	Deep waters	Most abundant, targeted in Mack Days.
Bull Trout	Native	Cold, clean waters	Protected, must be released if caught.
Westslope Cutthroat Trout	Native	Tributaries & cooler lake areas	Montana's state fish, fly fishing favorite.
Lake Whitefish	Introduced	Deep & spawning in shallow waters	Good for fall fishing, excellent table fare.
Yellow Perch	Introduced	Shallow bays	Great for beginners, easy to catch.
Northern Pike	Introduced	Weedy, shallow areas	Aggressive predators, limited population.
Smallmouth Bass	Introduced	Rocky shorelines	Sport anglers' favorite, good summer catch.
Largemouth Bass	Introduced	Southern bays & vegetated zones	Less common, topwater lure responsive.
Rainbow Trout	Stocked/Occasional	Tributaries & some lake areas	More common outside main lake.
Kokanee Salmon	Formerly Present	Historic population	Extirpated due to lake trout and mysis shrimp.