Bertha Lake

On the LakeGrade rubric, Bertha Lake pulls an A: clarity at 17.2 ft and 13 µg/L of phosphorus 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, Bertha Lake reads as oligotrophic — nutrient-poor, clear, and ecologically more sensitive to disturbance than richer lakes. At 64 ft of maximum depth, Bertha Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 337 acres, Bertha Lake fits the Minnesota median for monitored lakes, with 3.9 miles of shoreline. Among the 120 graded lakes in Crow Wing County, Bertha Lake sits at rank 37, above the county median.

Bertha 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 fishery includes walleye alongside the lake's other 22 documented species — a notable draw for Minnesota anglers. The lake lacks a documented public access point, so visitor use is limited. Ice-out has been recorded 10 times at Bertha Lake, with a median around Apr 18. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.