Marion Reservoir algae bloom status

Marion Reservoir algae bloom history

The Kansas Department of Health and Environment has tested Marion Reservoir 330 times since 2011, usually after someone reported a possible bloom. 129 samples (39%) reached at least Watch level, and 75 reached Warning level or higher.

6 samples reached Hazard level, KDHE's highest, where it recommends closing all or part of the lake.

The highest microcystin result was 5,000 µg/L, about 625 times KDHE's Warning threshold of 8 µg/L.

Blooms have been recorded every year for the last 6 years in the data.

That puts Marion Reservoir 1st of the 145 Kansas lakes on this site for the number of years with blooms.

When do algae blooms happen at Marion Reservoir?

At Marion Reservoir, reports are most often logged in May, June and July.

About 98% of reports fall between May and September, when warm, calm, sunny weather lets blue-green algae multiply.

Blooms can appear, move with the wind and fade within hours or days, so the time of year is only a guide.

Recent Marion Reservoir algae reports

Recent reports came from 3 different locations around Marion Reservoir, including Marion Lake Marion Cove, Marion Lake Hillsboro Cove and Marion Lake Cottonwood Point. A bloom in one cove or beach doesn't mean the whole lake is affected, and conditions can differ a short distance away.

What the Kansas results mean

KDHE sets each advisory from lab results or what staff see at the lake. Samples on this page are labelled with the level their results reached.

Watch

A bloom is visible, microcystin is above 4 µg/L, or there are more than 80,000 cyanobacteria cells per mL. Avoid algae and keep people and pets from swimming near it or drinking the water.

Warning

Microcystin above 8 µg/L, more than 250,000 cells per mL, or heavy surface scum. Avoid all contact with the water, including fishing and boating.

Hazard

Microcystin above 2,000 µg/L or more than 10 million cells per mL. KDHE recommends closing all or part of the lake and sometimes the shore nearby.

Is Marion Reservoir safe for dogs?

Dogs are at the greatest risk from toxic algae. They swallow water while swimming, eat scum on the shore and lick algae off their fur afterwards, and a small amount can kill a dog within hours. With blooms recorded in 14 different years here, take particular care at Marion Reservoir in May, June and July.

• Keep your dog on a lead near water that looks green, scummy, foamy or discoloured, and away from algae washed up on the shore.
• If your dog gets in, rinse it straight away with clean water and don't let it lick its coat.
• Call a vet immediately if your dog vomits, drools, has diarrhoea, staggers, shakes or seems weak after being near the water.

Read the full guide to toxic algae and dogs: symptoms, what to do in the first minutes and how vets treat it.

Health effects of toxic algae

Blue-green algae (cyanobacteria) can produce toxins that affect the liver, nervous system and skin. Swallowing water during a bloom can cause stomach pain, vomiting and diarrhoea. Skin contact can cause rashes, and breathing spray from the water can irritate the eyes, nose and throat. Children are at higher risk because they are smaller and more likely to swallow water.

How to spot a bloom

Toxic blooms can look like pea soup, spilled paint or green streaks on the surface, and they can also be blue, brown, white or red. Scum often collects along the shore downwind. If you can't see your feet in knee-deep water, or you aren't sure, stay out.

Don't drink untreated lake water, and don't boil it to make it safe: boiling doesn't destroy algal toxins. If you feel unwell after contact with the water, contact a doctor or Poison Control on 1-800-222-1222.

Nearby lakes with algae reports

• Marion County State Fishing Lake11 km away, 78 reports, last in 2026
• Herington Reservoir31 km away, 9 reports, last in 2022
• Herington City Lake33 km away, 32 reports, last in 2026
• McPherson County State Fishing Lake35 km away, 14 reports, last in 2015
• Harvey County East Lake38 km away, 73 reports, last in 2024

All Marion County lakes with algae reports

Questions about Marion Reservoir

Is there algae in Marion Reservoir right now?

Kansas has no current advisory for Marion Reservoir. The most recent sample, on 3 August 2026, was below advisory levels (microcystin 0.4 µg/L). This site checks KDHE's advisory list every day, but lakes are only sampled after a bloom is reported, so for today's conditions check the KDHE algae bloom map and the signs at the shore.

When was the last algae bloom at Marion Reservoir?

The most recent entry in Kansas's data is from 3 August 2026: a sample below advisory levels (microcystin 0.4 µg/L).

Has Marion Reservoir had toxic algae before?

Yes. Blooms are recorded in 14 of the 16 years from 2011 to 2026, most often in May, June and July.

Can dogs swim in Marion Reservoir?

Keep dogs out of the water whenever a bloom is reported or the water looks green, scummy or discoloured. Dogs are the animals most often killed by algal toxins because they swallow water and lick their fur. If your dog swims in water that might have algae, rinse it with clean water and call a vet if it vomits, drools, staggers or seems weak.

Can you eat fish caught in Marion Reservoir during a bloom?

If you keep fish caught during a bloom, health agencies advise removing the guts and liver and rinsing the fillets in clean water before cooking, because toxins collect most in the organs. Some agencies advise not eating fish from an active bloom at all, so follow local guidance.