First HABs confirmed on Seneca Lake

Bill Roege, HABs Director,  Seneca Lake Pure Waters Association
Confirmed and suspected Harmful Algal Blooms (HAB) on Seneca Lake.

FINGER LAKES – Seneca Lake saw its first confirmed Harmful Algal Blooms (HABs) of the season at the end of August. It kicked it off Aug. 26-27 with three confirmed blooms (plus one suspicious bloom) in the northeast near Sampson State Park’s marina. After a northerly wind on Friday, Aug. 27, Saturday saw two confirmed blooms (plus one suspicious bloom) in the southern end.

Two brief blooms were also reported on Keuka Lake near Penn Yan the same week, following heavy storm runoff and high water.

When we say something is confirmed, it means we have evidence that convinces us that what the volunteer saw was, in fact, a bloom. Sometimes we do not get a photo, so we cannot make an independent assessment. Other times, the photographic evidence is not conclusive or the amount of cyanobacteria does not appear to be enough to meet the DEC bloom criteria. The cyanobacteria can be visible before it is dense enough to be considered a “bloom”. 

In past years, the first week of September usually had a sudden spike in blooms. Given many people will want to be in the water for Labor Day weekend, extra care should be taken to “look before your leap.” If in doubt, do not go in the area where there are visible blooms. 

From the rains, we have seen a lot of debris and weeds in the lake. Duckweed has been something that is being mistaken for a HAB, possibly because it floats on the water and takes the form of “dots.” As a reminder, cyanobacteria blooms do not have mass; duckweed does. 

If you take a stick and dip it in a HAB, it will break up. Duckweed will move around, but the dots will stay intact. Do not put a bare hand into a suspect area. 

Check the Pure Waters HAB website ( for the latest information. 

What do blooms look like?

We will provide some photos in each Bloom Watch to help everyone better identify blooms.

A very dense harmful algal bloom in a marina.
An HAB near a shoreline,  showing a more typical early season pattern.

These two photos are from the last week in August. The first one shows a very dense bloom in a marina. Very still, shallow water can get very warm and the blooms have no wave action or drift to break them up. The second photo is near a shoreline and shows a more typical early season pattern. What was interesting on both are the colors. Both photos seem washed out toward a white rather than green tint. Note in the second photo the leaves are also white.

As a reminder, always assume a bloom, or any visible cyanobacteria, is toxic and stay away.  

HAB Facts: What you need to know

• Exposure to any cyanobacteria HABs can cause health effects in people and animals when water with blooms is touched, swallowed, or when airborne droplets are inhaled. This is true regardless of toxin levels; some blue-green algae produce toxins, while others do not. Exposure to blooms and toxins can cause symptoms such as diarrhea, nausea or vomiting; skin, eye or throat irritation and allergic reactions or breathing difficulties.

• Because blue-green algal bloom conditions change rapidly over time, the best prevention is to take steps to avoid waters with visible blooms: people, pets, and livestock should avoid areas with blooms or surface scums, or water that is noticeably discolored. 

• Avoid blooms when swimming, boating, fishing, and don’t eat fish caught from areas of water with blooms.

• If you or your pets are exposed to blue-green algal blooms, stop using the water and rinse off with clean water.

• Consider medical attention for people and animals if symptoms such as diarrhea, nausea, or vomiting; skin, eye, or throat irritation; and allergic reactions or breathing difficulties occur after contact with surface waters with blooms.

• Never drink untreated surface water. Even if you treat it in your home with water filtration, chlorine, ultraviolet (UV) light, or other treatment; it’s still not protected from blue-green algae and toxins.

• If you would like to see where HABs are occurring in NY State, visit the DEC Website at Their map is at:

• One of the best things you can do to stay on top of this situation is to visit the Seneca Lake Pure Waters website frequently at It has the most current information. In addition, if you live on the lake, it might be a good idea to check with neighbors and determine who your local Shoreline Survey Volunteer is. All of Pure Waters volunteers are a wealth of information and a good person to know. Our 120+ volunteers are well distributed around the lake and many residents have regular conversations with our volunteers as they survey our shores on a regular basis.