Big Butternut Lake

Big Butternut Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade. Phosphorus is the parameter holding the grade back — runoff from the surrounding watershed appears to keep nutrient levels elevated through the summer.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. The lake bottoms out at 19 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. At 384 acres, Big Butternut Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Within the 77 graded lakes of Polk County, Big Butternut Lake sits at rank 64, near the bottom of the county list.

An invasive species record — Banded Mystery Snail — has been logged at Big Butternut Lake; Wisconsin DNR maintains the official infested-waters list. The fishery includes walleye alongside the lake's other 4 documented species — a notable draw for Wisconsin anglers. A documented public access point at Big Butternut Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.