Clearest Lakes in the US

Crater Lake in Oregon is widely regarded as the clearest lake in the US, with Secchi clarity historically measured near 100–140 feet. Among US lakes with an A–F letter with standardized data, the clearest is Adams Lake in Vilas County, WI, where a Secchi disk stays visible to roughly 100 feet down (overall grade null).

Clarity is measured with a Secchi disk — a weighted black-and-white disk lowered on a line until it can no longer be seen. The depth in feet at which it vanishes is the Secchi reading. Deeper readings mean clearer water. It is the oldest and most widely collected water-quality measurement, which is why it anchors lake clarity rankings.

Clarity is driven by what is suspended in the water: algae (fed by phosphorus), sediment from runoff and shoreline erosion, and tannins from wetlands. The clearest lakes tend to be deep, spring-fed or seepage lakes with low nutrient inputs and protected, forested shorelines. Shallow lakes ringed by farmland or development almost always read murkier.

Not on clarity alone. Secchi tracks algae and sediment, not E. coli, cyanotoxins, or a posted beach closure. The ranking is water clarity, not a swimming clearance. Always check current local advisories before swimming.