Charles Mill Reservoir Water Temperature
Charles Mill Reservoir in Ashland County, Ohio averages about 78°F at the surface in summer — warmest in Aug (~79°F) and coldest in Oct (~65°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 135 field readings (2010–2021) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Charles Mill Reservoir warm enough to swim?
Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Want more than temperature? Charles Mill Reservoir scored F on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
Water temperatures at nearby Ohio lakes
Summer average ~79°F
Summer average ~76°F
Summer average ~79°F
Summer average ~79°F
Summer average ~79°F
Summer average ~66°F
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Frequently asked questions
What is the water temperature of Charles Mill Reservoir?
Charles Mill Reservoir has a typical summer surface temperature of about 78°F. It is usually warmest in August (around 79°F) and coldest in October (around 65°F). These are typical values by month from 135 EPA Water Quality Portal field readings (2010–2021), not a live reading.
When is Charles Mill Reservoir warmest?
Surface water at Charles Mill Reservoir is typically warmest in August, 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 Charles Mill Reservoir warm enough to swim?
At its typical summer peak of about 78°F, Charles Mill Reservoir rates as "comfortable" for swimming. Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Where does this Charles Mill Reservoir 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 — 135 readings from 2 monitoring stations between 2010 and 2021. 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.