Typical water · long-term monitoring averages
Best lakes to swim in August
Well-loved U.S. lakes where the surface water usually averages 70°F or warmer in August. Looking for the coast? See the best beaches in August.
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Algae season: blooms are more likely in warm, slow-moving, nutrient-rich water, per the CDC. Stay out of water that looks discolored or scummy, follow posted advisories, and keep pets out.
How we pick
We start from U.S. lakes rated 4.3★ or higher across 100+ Google reviews and look for a monitoring station named for the same lake in the Water Quality Portal (USGS, EPA and state agencies). We keep only lakes with a swim beach or swimming allowed — checked against the operator’s rules where the listing doesn’t say — which leaves 62. Rules change and some areas close seasonally, so check with the park or lake operator first. Each month’s figure averages near-surface readings since 2010, counting the warmest reading of each sampling day, and needs at least three sampling days. A lake makes the list at 70°F or warmer — below that, sudden entry risks cold shock — ranked by a review-weighted rating, at most two per state. Monitoring is irregular, so treat these as typical, not exact.