Rock

Rock lake is 341 acres with a maximum depth of 13 feet. A targeted panfish assessment was conducted on 5/20/2025. A total of 14 Bluegill were sampled, resulting in a trap net catch rate of 2.3 per net. Bluegill averaged 5.7 inches with fish up to 8.5 inches observed. Fish ranged from 2 to 5 years old. Bluegill averaged 6.8 inches in 4 years and was up from the previous estimate in 2017 (4.9 inches at age 4). Only 2 Black Crappie were sampled, both measuring 10.2 inches. Both fish were 4 years old and displayed good growth when compared to historic growth rates (2017 mean length at age 4 was 6.8 inches). It's important to note that water temperature was between 48 and 50 degrees Fahrenheit during the assessment, however it was likely in the upper 50's and low 60's a few days prior. A steady week of cold weather and a sharp drop in water temperature prior to the assessment likely resulted in the low catch rates we observed.

This survey was conducted on 2/27/2025 to gauge the likelihood of a winterkill occurring on Rock Lake. Winter dissolved oxygen levels were good for Rock Lake and likely tolerable based on this survey with 5.6 ppm below the ice and 1.7 ppm near the bottom. Therefore, it seemed unlikely for any significant winterkill to occur in spring 2025.

Rock Lake is located 6 miles west of McGregor in east central Aitkin County. The public access is located on the north side of this moderately developed lake. This 300 acre lake is shallow and has a history of partial winterkills. The recent strong winterkills probably took place the winters of 1996-1997, 2012-2013 and 2013-2014; although, as this report was prepared we did receive another report of a likely kill beginning in February 2018. Partial winterkills are likely to have occurred in other years too, but were never reported or documented. Winterkills are not necessarily a bad thing and historically were fairly common in Minnesota. In recent years, winters have not been as harsh and winterkills have not been as prevalent on a statewide scale. Partial winterkills are usually good for lakes particularly when it comes to bluegills. Following a winterkill there are typically enough survivors to repopulate the lake and growth rates tend to be very good for some time. As densities increase with the addition of each new year class, the survival decreases and growth rates slow. The lake then winterkills again, thereby decreasing density, and the whole process of high survival and fast growth repeats itself. When these lakes go several years without a winterkill, they can provide for excellent fisheries. As of 2017, black crappie, bluegill and northern pike populations were healthy and rebuilding. Largemouth bass were not sampled in 2017, but are known to inhabit the lake and sometimes take longer to recover from winterkill situations. It appeared fish populations were beginning to recover from the most recent known winterkills in 2012-13 and 2013-14. The previous survey, in 2007, showed that populations of gamefish including northern pike, black crappie, bluegill and yellow perch were present in good numbers. The 2017 assessment showed much lower numbers for those same species, but they were mostly still within the normal ranges for this lake. Sizes were overall pretty good, especially for the panfish. Yellow perch numbers did go down somewhat since 2007, although they were still above normal levels for this lake type. Good perch populations are often a key component to quality fisheries. While no AIS are present at this time, extra diligence is in order to prevent the spread from other waters. Lake users and shoreland owners should be remember to follow AIS rules for boating and installing/removing dock equipment.

Based on Minnesota DNR survey data, anglers target Yellow Perch, Northern Pike, Bluegill, Black Crappie, and Pumpkinseed in Rock. See the full species list above for catch rates, size structure, and quality scores.

Minnesota DNR records list public access for Rock. Check the DNR LakeFinder page for the launch type and directions before you go.

Rock has a maximum depth of 13 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in Rock is from 2017. Surveys this old should be treated with some caution — fish populations change over time.

No invasive species are on record for Rock in Minnesota DNR data. Always clean, drain, and dry your equipment to help keep it that way.