Fenske Lake is in Ecological Lake Class 10, which consists of 76 lakes in northeast Minnesota that are small and have very soft (unmineralized) water. Fenske Lake has clearer water and a more irregular shoreline shape than most of the lakes in this lake class. Fenske Lake ranks as mesotrophic-to-eutrophic according to Carlson's Trophic State Index.
Fenske Lake was thermally stratified on 06/07/2007 with a surface temperature of 63 F and a bottom temperature of 42 F. Adequate oxygen for fish (more than 2 ppm) was present to a depth of 33 ft, where the temperature was 43 F. Fenske Lake has three inlets; two drain local swamps and the third, from Little Sletten Lake, has beaver dams that limit fish movement. The outlet, to Everett Lake, also has beaver dams that limit fish movement. Aquatic plant growth is sparse in the main basin of Fenske Lake, primarily because the shoreline is rocky and drops off quickly. Aquatic plant growth is lush in the shallow east and west ends of the lake, where they grow to a depth of 9 ft; watershield, waterlilies, floatingleaf burreed, and bladderwort are the most common plants. Lake bottom substrates along the shoreline of Fenske Lake are mostly ledge rock, boulder, and rubble in the main basin, and muck or silt in the shallow east and west ends.
There is a public access with a gravel boat ramp off the Echo Trail (CSAH 116), and portages to Little Sletten and Everett Lakes. About a third of the shoreline of Fenske Lake is in private ownership, primarily along the north shore. Riparian development increased from one resort with 12 cabins, a girl scout camp, and a U.S. Forest Service campground in 1960; to one resort with 7 cabins, the Forest Service campground, and 6 private cabins in 1979; and to two resorts with 9 cabins, the Forest Service campground (with 16 campsites), and 7 private cabins in 2007.
Fish sampling in the 2007 fisheries lake survey was done with six gillnets, nine standard trapnets, and four small mesh (1/4" bar) trapnets used for catching small fish. Nine previous fisheries investigations, dating back to 1960, used 3-6 gillnets and 2-10 trapnets. Most of these investigations were done in July or August, but the 2007 investigation was done in June due to scheduling considerations and because panfish are more easily captured early in the summer. Most of the trapnets were set in the shallow east and west basins of the lake, while the gillnets were set in the deeper main basin of the lake.
The total catch of fish (all species combined) in the gillnets in 2007 of 3 fish/net (6 lb/net) was in the first quartile for this lake class and was similar to the median total catch of 5 fish/net (8 lb/net) in all investigations on this lake. Lake Class 10 is one of the least productive lake classes in northeast Minnesota, in terms of gillnet catches of fish. The gillnet catch in 2007, as in previous investigations on this lake, was dominated by northern pike.
The total catch of fish in the trapnets in 2007 of 24 fish/net (10 lb/net) was very similar to the median total catch in all investigations on this lake of 21 fish/net (4 lb/net). The trapnet catch in 2007, as in previous investigations on this lake, was dominated by bluegill sunfish.
Northern pike numbers in 2007 (2.3/gillnet) were in the second quartile for this lake class, but were higher than the median catch of 1.2/gillnet in all investigations on this lake. Fair numbers of pike (2.4/net) were also caught in the trapnets in 2007. Pike sizes in the gillnets averaged 22.6" (2.6 lb), which was in the third quartile for this lake class, but was smaller than the average size of 28.6" in all investigations on this lake. The largest pike in 2007, caught in a trapnet, was 32.9". Pike growth was normal by area standards.
Bluegill numbers in 2007 (18.7/trapnet) were in the third quartile for this lake class, and were similar to the median catch of 16.3/trapnet in all investigations on this lake. Bluegill sizes in 2007 averaged 6.4" (0.2 lb), which was in the third quartile for this lake class and was larger than the average bluegill size of 5.8" in all investigations on this lake. The largest bluegill in 2007 was 8.7". Most bluegill were ages five and six, and fair numbers of young-of-year bluegill were caught in the small mesh trapnets. Bluegill growth was slower than normal (in the first or second quartile, depending on the age) by area standards.
Black crappie numbers in 2007 (1.4/trapnet), as in previous investigations, were quite low. Large crappie (up to 12") were caught in most investigations on this lake, but the largest crappie in 2007 was 10.8".
Bass populations in Fenske Lake are likely more abundant than indicated by the net catches. Bass are "net-shy" and tend to avoid standard sampling nets. Some young-of-year largemouth were captured in the small mesh trapnets in 2007.
Most of the game fish examined in 2007 were free of diseases or parasites. A few bluegill were infected with neascus. Neascus (black spot) is a common parasite that is native to the area. It cannot infect humans, is often removed by filleting fish, and is killed at temperatures used to cook fish.