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LakeQuality
A

Agency Bay Lake

Cass County, MinnesotaOligotrophic

On the LakeGrade rubric, Agency Bay Lake pulls an A: clarity at 15.2 ft and phosphorus readings still being added put it in the top bracket for Minnesota. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

Trophically, Agency Bay Lake reads as oligotrophic — nutrient-poor, clear, and ecologically more sensitive to disturbance than richer lakes. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. Among the 133 graded lakes in Cass County, Agency Bay Lake sits at rank 40, above the county median.

Agency Bay Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The state fisheries records do not list documented species for Agency Bay Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. A documented public access point at Agency Bay Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The lake has a long ice-out record — 71 observations on file, with a median ice-out around Apr 28. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-09-07. Grade methodology: LakeGrade methodology.

Swimming Safety

Excellent for swimming, crystal clear water with minimal algae

Water Quality Grade: A, Excellent

Crystal clear, you can see 15.2 ft down. Chlorophyll-a: 2.7 µg/L. Trophic State Index: 39.

MetricValueGrade
Water Clarity (Secchi Depth)15.2 ftA
PhosphorusNo data
Chlorophyll-a (Algae)2.7 µg/LA
Trophic State Index (TSI)39Oligotrophic

Low nutrients, clear water, excellent for swimming

Invasive Species

Eurasian watermilfoilstarry stonewortzebra mussel

Water Quality Trend: Improving

Based on 5 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Improving+0.224 m/yr5
Phosphorus Stable+0.1 µg/L/yr5
Chlorophyll-a Improving-0.5 µg/L/yr2

Ice Season

Historical ice data from Minnesota DNR (74 observations).

Typical Ice-Out
Apr 28
Typical Ice-In
Nov 14

Estimated open water season: 200 days

EarliestLatest
Ice-Out1945-04-09 (1945)1950-05-23 (1950)
Ice-In2018-11-13 (2018)2021-11-25 (2021)

Most recent ice-out: 2022-05-08

Location

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County Ranking

Ranked #40 of 133 lakes in Cass County

Nearby Lakes in Cass County

DNR Reports & Resources

Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Agency Bay Lake. 1 report on file.

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Ice data from Minnesota DNR Climate

Most recent sample: 2023-09-07

Monitoring stations: 1