Surprise Lake

On the LakeGrade scale Surprise Lake grades a B, with clarity at 8.0 ft and 13 µg/L of phosphorus placing it above the Wisconsin median. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Wisconsin norms.

Mesotrophic conditions dominate at Surprise Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. A maximum depth of 20 ft puts Surprise Lake in the middle of Wisconsin's depth distribution. Surprise Lake is small — 66 acres alongside partial shoreline records — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Surprise Lake sits at rank 40 of 62 in Oconto County, in the lower half of the local distribution.

An invasive species record — Purple Loosestrife — has been logged at Surprise Lake; Wisconsin DNR maintains the official infested-waters list. Walleye are documented at Surprise Lake, one of 4 fish species on record for the lake. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.