St. Louis Bay Lake Water Temperature
St. Louis Bay Lake in Douglas County, Wisconsin averages about 72°F at the surface in summer — warmest in Jul (~79°F) and coldest in May (~64°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 9 field readings (2025–2025) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is St. Louis Bay Lake warm enough to swim?
Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Want more than temperature? St. Louis Bay Lake scored D on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
Water temperatures at nearby Wisconsin lakes
Summer average ~73°F
Summer average ~72°F
Summer average ~70°F
Summer average ~65°F
Summer average ~74°F
Summer average ~74°F
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Frequently asked questions
What is the water temperature of St. Louis Bay Lake?
St. Louis Bay Lake has a typical summer surface temperature of about 72°F. It is usually warmest in July (around 79°F) and coldest in May (around 64°F). These are typical values by month from 9 EPA Water Quality Portal field readings (2025–2025), not a live reading.
When is St. Louis Bay Lake warmest?
Surface water at St. Louis Bay Lake is typically warmest in July, reaching about 79°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 St. Louis Bay Lake warm enough to swim?
At its typical summer peak of about 72°F, St. Louis Bay Lake rates as "comfortable" for swimming. Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Where does this St. Louis Bay 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 — 9 readings from 1 monitoring station between 2025 and 2025. 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.