08/26/2026
DOES YOUR POND/TANK WATER LOOK WEIRD OR COLORFUL?
What is a blue-green algae bloom?
Cyanobacteria (blue-green algae) are microscopic organisms that can be found in all types of water. The blooms may range in color from blue to bright green, brown or red and may resemble paint floating on the water.
Are there human and animal health concerns?
Some cyanobacteria can produce toxins that can be harmful to humans and animals. Swallowing low doses can cause gastroenteritis (vomiting and diarrhea) while higher doses may affect the nervous system and liver and even cause sudden death in animals.
To determine whether what you’re seeing are true algae or blue-green algae, you can conduct the jar or stick test.
These tests may help you determine if blue-green algae are present, but they do not tell you whether the blue-green algae are producing toxins. We can send your water sample to OADDL and have it tested.
The Jar Test
With gloves on, use a glass jar to collect a sample just below the surface of the water (avoid collecting just the top layer of scum).
Fill the jar about three-quarters full (leave room at the top for gas production). Wipe any scum off the outside of the jar and screw the lid on. Give it a shake.
Leave the jar in a location where the contents will not be disturbed.
After 2 or 3 hours, observe the jar to see where the algae have settled. Algae that sink to the bottom are likely true algae, and algae that form a greenish ring at the top of the water are likely blue-green algae.
A sturdy stick with algal material attached
The Stick Test
With gloves on, push a long, sturdy stick into the surface of the algal material and slowly lift it out of the water.
If the stick comes out looking like it has been dipped into a can of paint, the material is likely blue-green algae. If it comes out with long, green, hair-like strands or threads, the material is probably true algae (filamentous green algae).
