SwimZone

Lake · Preble County · OH

Is Acton Lake safe to swim?

Advisory

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

Updated July 22, 2026 · EPA CyAN satellite

Recent rain
1.0 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
807,947
cells/mL
Advisory over
100,000
cells/mL

Cyanobacteria 807,947 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 Acton Lake right now.

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

What's in the water at Acton Lake right now

As of July 22, 2026, Acton Lake in Preble County, Ohio is not recommended for swimming. Satellite imagery measured 807,947 cells/mL of blue-green algae on July 21, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 1.0 in, which can wash bacteria and nutrients into the water.

How this read is built

Blue-green algae at Acton Lake

Acton Lake is a lake in Preble County, Ohio covering about 0.9 sq mi, the 29th-largest of the 41 lakes SwimZone monitors in Ohio. Satellite imagery measured 807,947 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 Acton Lake

From EPA CyAN's satellite archive

2020: peak 1,103,832 cells/mL — above the 100,000 advisory level202021: peak 1,042,949 cells/mL — above the 100,000 advisory level212022: peak 701,105 cells/mL — above the 100,000 advisory level222023: peak 1,072,959 cells/mL — above the 100,000 advisory level232024: peak 1,346,304 cells/mL — above the 100,000 advisory level242025: peak 1,135,594 cells/mL — above the 100,000 advisory level2526Advisory100k 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, Acton Lake has reached blue-green algae advisory levels in 6 of them, most recently in August 2025. This is a lake that blooms most summers. Its highest recorded reading was 1,346,304 cells/mL in August 2024.

When to swim at Acton Lake

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 (6 of 7), historically peaking around August. 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 Acton Lake

Is it safe to swim in Acton Lake right now?
Acton Lake is not recommended for swimming today. Satellite imagery measured 807,947 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 Acton Lake have blue-green algae (cyanobacteria)?
Yes. Satellite monitoring measured 807,947 cells/mL of blue-green algae (cyanobacteria) at Acton Lake 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 Acton Lake?
No. Blue-green algae at Acton Lake is above the safe-contact threshold (807,947 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 Acton Lake have blue-green algae blooms?
Over 7 summers of satellite monitoring since 2020, Acton Lake has reached blue-green algae advisory levels in 6 of them, most recently in August 2025. This is a lake that blooms most summers. Its highest recorded reading was 1,346,304 cells/mL in August 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 Acton 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 Acton Lake, and a recent-rainfall overlay, all refreshed daily. It was last updated July 22, 2026.

Before you swim: the basics

Swim spots near Acton Lake

All Ohio →

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

WaterDistanceTodayAlgae readSampled
Cowan LakeLake · Clinton County47 miClear to swimNone detectedJul 21
William H Harsha LakeLake · Clermont County51 miAdvisory160,377 cells/mLJul 21
Kiser LakeLake · Champaign County59 miAdvisory1,839,344 cells/mLJul 21
Lake LoramieLake · Shelby County60 miAdvisory1,737,893 cells/mLJul 21
Clarence J Brown ReservoirReservoir · Clark County61 miClear to swimNone detectedJul 21
Grand LakeLake · Mercer County67 miAdvisory2,895,896 cells/mLJul 21