Arthur Lake is in Ecological Lake Class 10, which consists of 76 lakes in northeast Minnesota that are small and have soft (unmineralized) water. Arthur Lake is shallower than most of the lakes in this lake class. The water in Arthur Lake is bog stained brown and the water clarity appears to have increased over time.Arthur Lake ranks as mesotrophic according to Carlson's Trophic State Index with total phosphorus of 18 ppb, chlorophyll-a of 5.3 ppb, and Secchi water clarity of 2.8 m. Arthur Lake was thermally stratified on 08/09/2004 with a surface temperature of 69 F and a bottom temperature of 58 F. Adequate oxygen for fish (more than 2 ppm) was retained to a depth of 10 ft, where the temperature was 65 F. A winter oxygen check on 3/13/1986 showed a maximum of 5.0 ppm.Arthur Lake has two small inlets that drain local swamps. The outlet, to Isaac Lake, has no barriers to fish movement. Lake bottom substrates along the shoreline are gravel, silt, sand, and rubble. Aquatic plants grow to a depth of 7 ft; the most common plants are sedges, various pondweeds, water shield, water horehound, stonewort, and water lilies. Arthur Lake is mostly surrounded by private land and there is no designated public access on the lake. There is a State tax forfeited 40 acre parcel on the northeast corner of the lake. Dewees Road crosses private land just to the south of Arthur Lake. There is one seasonal cabin and one travel trailer on the eastern bay of Arthur Lake. Access for the 2004 fisheries lake survey was through private property.Fish sampling for the 2004 fisheries lake survey consisted of three standard survey gillnets, nine standard survey (3/4" bar mesh) trapnets, and four young-of-year (1/4" bar mesh) trapnets. Previous Fisheries lake surveys in 1966 and 1983 used three gillnets, four or five 3/4" bar mesh trapnets, and a shoreline seine (in 1966) and two 1/4" bar mesh trapnets (in 1983). Very few fish (only a few white sucker) were caught in the 1966 gillnets. It is possible the nets may have been set too deep (below 9 ft) in water that had little oxygen.Fish populations in 2004 were dominated by bluegill sunfish, followed by northern pike, walleye, and white sucker.Only one bluegill was caught (in a seine) in the initial lake survey in 1966. Bluegill numbers since then have increased greatly, to 16.0/trapnet in 1983 and to 29.3/trapnet in 2004. Bluegill sizes in 2004 averaged 5.4"; the largest bluegill was 8.6". Bluegill from eight year classes were captured, but there were relatively few age four bluegill (from the 2000 year class) present. Bluegill growth was slower than normal (in the first or second quartile, depending on the age) by area standards.Northern pike numbers in 2004 (3.7/gillnet) were in the third quartile for this lake class and were higher than the 1983 catch of 2.0/gillnet. Pike sizes in 2004 averaged 18.8" (1.8 lb), which was in the second quartile for this lake class. The largest pike captured in 2004 was 33.3". Pike recruitment was erratic and growth was slower than normal by area standards.Walleye numbers in 2004 (1.7/gillnet) were in the second quartile for this lake class and were similar to the 1983 walleye catch of 1.0/gillnet. Walleye sizes in 2004 averaged 17.8" (1.9 lb), which was in the third quartile for this lake class. The largest walleye, caught in a trapnet, was 22.4". The youngest walleye captured in 2004 was age three. Walleye growth appeared to be somewhat faster than normal (in the third quartile) by area standards.White sucker numbers in 2004 (2.7/gillnet) were in the second quartile for this lake class. Only one largemouth bass and one yellow perch were captured in the standard gillnets and trapnets in 2004, but good numbers of young-of-year largemouth and perch were caught in the small mesh trapnets. Other fish species were present in low numbers.Some of the bluegill, northern pike, and walleye examined in 2004 were infected with neascus. The single adult yellow perch examined in 2004 was infected with yellow grub. Neascus (black spot) and yellow grub are common parasites that are native to the area. They cannot infect humans, are often removed when the fish is filleted, and are killed at temperatures used to cook fish.