Flat Horn Lake is 7 miles northwest of Isabella in the Superior National Forest. The lake has a maximum depth of 7.5 feet and a Secchi disc is visible in the brown-stained water at that depth. There is a carry down access of approximately 100 feet suitable for canoes or small boats. There is a U.S. Forest Service maintained picnic area and a swimming beach and ski trail are adjacent to the access. The remainder of the shoreline is undeveloped and in a wild state.
The fish community in Flat Horn Lake is comprised of northern pike, walleye, bluegill, rock bass, yellow perch and pumpkinseed sunfish. Largemouth bass were stocked in Flat Horn Lake in the 1980s however the species has not been sampled in netting gear and it is uncertain if they are present at this time. The lake is managed primarily for northern pike and no stocking is needed.
In 2006 northern pike were sampled in average numbers as they have been in most of the assessments conducted on this lake. Mean size was 2.1 lb which is normal for the lake class and similar to the mean size in other assessments on this lake. Northern pike up to 29.3 inches were collected however most of the fish were smaller than 22 inches.
Flat Horn Lake is not managed for walleyes. However, the species maintains a small population through natural reproduction. Walleyes were sampled in relatively low numbers in 2006, which is normal for this lake. Mean weight of walleyes collected in past assessments has been average for the lake class; however, mean weight increased in this assessment (2.3 pounds) and was above average. All the walleyes collected in this assessment were between 17 and 20 inches.
Bluegills had not been sampled in Flat Horn Lake for over 20 years, but one was captured in 2006. In recent years bluegills have become fairly well established in adjoining Gegoka Lake, and may be expanding into Flat Horn Lake, though at this time it appears that bluegill numbers are low.
Yellow perch were sampled in good numbers, including a few fish between 10-12 inches. However, most of the fish were smaller than 8 inches and probably too small to interest most anglers.