Lake Four (Seth Lake) is a shallow lake located approximately 5 miles southeast of Aitkin in a watershed of pastureland, rolling hardwoods, and a spruce wetland. The lake has an average depth of 8 feet and a maximum depth of 31 feet. There is no public access on the lake, however, there is private access through a campground on the east side of the lake.
In the early 1990's, Lake Four was part of a management project that involved the removal of a large number of northern pike (2,681), and the stocking of a large number of yellow perch (38,113). The goal of the project was to improve the size structure of northern pike and bluegill populations. Theoretically, had the perch population flourished, they would have provided a forage base for the northern pike as well as predation pressure on an overabundant and stunted population of bluegills. The experiment was short lived and unsuccessful. The last two surveys (1999, 2009) have shown the fish community to be much the same as before the project.
Northern pike abundance increased to 14 fish per gill net lift, which is high compared to other lakes of this type, and is the highest that has been observed on Lake Four. The average size of the northern pike was 20.6 inches, which is similar to observations made in 1996 and 1999. The largest northern pike sampled measured nearly 36 inches.
Bluegill abundance was within the normal range for this type of lake at 22.2 fish per trap net. The average size of the bluegills has remained small, fluctuating between 4.6 inches in 1991 and 5.2 inches in 2009. The bluegill in Lake Four may not be able to grow beyond these sizes because of fishing pressure that targets the largest individuals.
The black crappie abundance index of 4.0 per gill net is stable at a level that is normal for this lake class. The average size of the crappies was over 8 inches long with individuals measuring over 10 inches. The 2009 sample had fish from five different year-classes, which suggests consistent recruitment.
Lake Four continues to support a population of largemouth bass with higher than average abundance based on the gillnet catch rates in 2009. The size structure of the population appears healthy, with a maximum size observed approaching 19 inches and an average length of around 14.5 inches.
Angler behavior has the greatest potential for restructuring or protecting existing fish populations in Lake Four. For example, selectively harvesting smaller northern pike and voluntarily releasing pike over 24 inches is encouraged. Anglers are also encouraged to release the larger panfish and bass. Recycling these large fish has the greatest potential to improve the size structure of anglers' catches.