Is South Holston Lake safe to swim?

As of July 20, 2026, South Holston Lake in Sullivan County, Tennessee is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.7 in, which can wash bacteria and nutrients into the water.

How this read is built

South Holston Lake is a lake in Sullivan County, Tennessee covering about 11.7 sq mi, the 9th-largest of the 20 lakes SwimZone monitors in Tennessee. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Larger, warmer waters like this can hold a bloom for weeks once nutrients and calm weather line up.

Blue-green algae (cyanobacteria) blooms are most common from midsummer into early fall, when the water is warm, calm, and rich in nutrients from runoff. They can produce toxins that make people sick and can be rapidly fatal to dogs, so skip water that looks green, scummy, or like spilled paint, and keep children and pets out of it.

Over 7 summers of satellite monitoring since 2020, South Holston Lake has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.

Is it safe to swim in South Holston Lake right now?

South Holston Lake is clear to swim today. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.

Does South Holston Lake have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at South Holston Lake as of July 19, 2026 (below the satellite's roughly 10,000 cells/mL detection limit). Cyanobacteria can still appear within hours in warm, calm, nutrient-rich water, so look before you swim.

Can dogs swim in South Holston Lake?

No bloom is detected at South Holston Lake today, but dogs are much more vulnerable to blue-green algae than people, and blooms can form within hours. Always keep dogs away from water that looks green, scummy, or discolored, and rinse them off after swimming.

How often does South Holston Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, South Holston Lake has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.

How many Tennessee lakes and beaches are unsafe for swimming today?

Today, 4 Tennessee waters are above a safe-contact threshold and 0 more warrant caution, out of 24 monitored waters SwimZone tracks in the state.

How is South Holston Lake's water quality measured?

SwimZone builds this read from EPA CyAN satellite imagery for blue-green algae, official beach and fecal-bacteria advisories where a program monitors South Holston Lake, and a recent-rainfall overlay, all refreshed daily. It was last updated July 20, 2026.