SwimZone

Lake · Madison County · OH

Is Lake Choctaw safe to swim?

Advisory

Blue-green algae is above the safe-contact threshold.

Updated July 22, 2026 · EPA CyAN satellite

Recent rain
6.7 in
Water type
Lake
Last updated
Jul 22
Bacteria
E. coli, fecal
Not monitored
Tested
Not monitored

No bacteria advisory or sampling for this water.

Blue-green algae
cyanobacteria
Advisory
Tested
1,465,895
cells/mL
Advisory over
100,000
cells/mL

Cyanobacteria 1,465,895 cells/mL (satellite, 7-day max), imaged 2026-07-21.

Sampled Jul 21 · EPA CyAN satellite

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There's an advisory on Lake Choctaw right now.

Get an alert the day it clears, and every time a new one goes up.

What's in the water at Lake Choctaw right now

As of July 22, 2026, Lake Choctaw in Madison County, Ohio is not recommended for swimming. Satellite imagery measured 1,465,895 cells/mL of blue-green algae on July 21, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 6.7 in, which can wash bacteria and nutrients into the water.

How this read is built

Blue-green algae at Lake Choctaw

Lake Choctaw is a lake in Madison County, Ohio. Satellite imagery measured 1,465,895 cells/mL of blue-green algae on July 21, 2026, above the 100,000 cells/mL advisory threshold.

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.

Bloom history at Lake Choctaw

From EPA CyAN's satellite archive

2020: peak 1,168,269 cells/mL — above the 100,000 advisory level202021: peak 1,787,899 cells/mL — above the 100,000 advisory level212022: peak 2,307,932 cells/mL — above the 100,000 advisory level222023: peak 1,642,037 cells/mL — above the 100,000 advisory level232024: peak 2,374,340 cells/mL — above the 100,000 advisory level242025: peak 1,737,893 cells/mL — above the 100,000 advisory level252026: peak 1,168,269 cells/mL — above the 100,000 advisory level26Advisory100k cells/mL

Each bar is that summer's peak satellite reading (log scale). The red cap is the part above the advisory level.

Over 7 summers of satellite monitoring since 2020, Lake Choctaw has reached blue-green algae advisory levels in 7 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 2,374,340 cells/mL in July 2024.

When to swim at Lake Choctaw

It is currently peak season for blue-green algae, when warm, calm water lets blooms form fastest. This lake has bloomed in most monitored summers (7 of 7), historically peaking around July. Early summer, before the water fully warms, has generally been the safer window here; check the current read before you go either way.

Frequently asked: swimming in Lake Choctaw

Is it safe to swim in Lake Choctaw right now?
Lake Choctaw is not recommended for swimming today. Satellite imagery measured 1,465,895 cells/mL of blue-green algae on July 21, 2026, above the 100,000 cells/mL advisory threshold. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.
Does Lake Choctaw have blue-green algae (cyanobacteria)?
Yes. Satellite monitoring measured 1,465,895 cells/mL of blue-green algae (cyanobacteria) at Lake Choctaw on July 21, 2026, above the 100,000 cells/mL advisory level. Avoid swimming and keep children and pets out of the water.
Can dogs swim in Lake Choctaw?
No. Blue-green algae at Lake Choctaw is above the safe-contact threshold (1,465,895 cells/mL on July 21, 2026). Cyanobacteria toxins can be rapidly fatal to dogs, which swallow it while swimming and lick it from their fur. Keep dogs out of the water and away from any scum along the shore.
How often does Lake Choctaw have blue-green algae blooms?
Over 7 summers of satellite monitoring since 2020, Lake Choctaw has reached blue-green algae advisory levels in 7 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 2,374,340 cells/mL in July 2024.
How many Ohio lakes and beaches are unsafe for swimming today?
Today, 33 Ohio waters are above a safe-contact threshold and 32 more warrant caution, out of 101 monitored waters SwimZone tracks in the state.
How is Lake Choctaw'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 Lake Choctaw, and a recent-rainfall overlay, all refreshed daily. It was last updated July 22, 2026.

Before you swim: the basics

Swim spots near Lake Choctaw

All Ohio →

Of the 6 monitored waters nearest Lake Choctaw, 4 are flagged today.

WaterDistanceTodayAlgae readSampled
Clarence J Brown ReservoirReservoir · Clark County13 miClear to swimNone detectedJul 21
Deer Creek LakeLake · Pickaway County27 miAdvisory662,435 cells/mLJul 21
Kiser LakeLake · Champaign County30 miAdvisory1,839,344 cells/mLJul 21
Williams LakeLake · Delaware County33 miClear to swimNone detectedJul 21
Hoover ReservoirReservoir · Delaware County35 miAdvisory471,306 cells/mLJul 21
Delaware LakeLake · Delaware County38 miAdvisory1,103,832 cells/mLJul 21