Rock Lake Water Temperature
Rock Lake in Jefferson County, Wisconsin averages about 77°F at the surface in summer — warmest in Jul (~80°F) and coldest in Mar (~40°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 14 field readings (2024–2026) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Rock Lake warm enough to swim?
Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Want more than temperature? Rock Lake scored A on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
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Frequently asked questions
What is the water temperature of Rock Lake?
Rock Lake has a typical summer surface temperature of about 77°F. It is usually warmest in July (around 80°F) and coldest in March (around 40°F). These are typical values by month from 14 EPA Water Quality Portal field readings (2024–2026), not a live reading.
When is Rock Lake warmest?
Surface water at Rock Lake is typically warmest in July, reaching about 80°F. Lake surface temperature lags air temperature by several weeks, so the warmest water usually arrives in mid-to-late summer even though the hottest air can come earlier.
Is Rock Lake warm enough to swim?
At its typical summer peak of about 77°F, Rock Lake rates as "comfortable" for swimming. Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Where does this Rock Lake water temperature data come from?
Every temperature on this page is a typical (climatological) value computed from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal — 14 readings from 1 monitoring station between 2024 and 2026. They describe what is typical for each month, not the temperature right now.
About this data
Water temperatures are a climatology — the typical value for each month, averaged from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal. They tell you what to expect, not the temperature at this moment. Actual conditions vary with recent weather, depth, and time of day.