Didymo Alert: Nuisance & Invasive Species Found in Catskills Streams and Rivers

Didymo Alert

What is didymo?

Didymo covered rock.

Didymo (Didymosphenia geminata), also known as "rock snot," is a non-native invasive microscopic algae (diatom) that can produce large amounts of stalk material to form thick brown mats on stream bottoms. Didymo threatens aquatic habitat, biodiversity and recreational opportunities. Native to northern North America and Europe, didymo has rapidly expanded its range, invading streams in several western states before moving east. Didymo has been found in several major New York water-based recreational rivers.

Historically, didymo has been found in cool, clear, nutrient poor waters but has expanded its worldwide distribution to include nutrient rich waters. Rivers with stable, regulated flows are particularly at risk.

How do I know if I find didymo?

  • Color - tan, brown or white (not green); may form long white "tails"
  • Texture - like wet wool (not slimy)
  • Strength - firmly attached; does not fall apart when rubbed between fingers

What are the Impacts of didymo?

Unlike many other aquatic invasive plants, didymo grows on the bottom of both flowing and still waters. It is characterized by the development of thick mat-like growths (blooms), which can last for months, even in fast flowing streams. During blooms, these mats may completely cover long stretches of stream beds, altering stream conditions and choking out many of the organisms that live on the stream bottom, which can affect trout and other fish by limiting their food. For the recreational user, footing can become very difficult due to the heavy growths.

Where has didymo been found in The Catskills?

Didymo has been confirmed in the following rivers in the Catskills:

  • East Branch Delaware River below Pepacton Reservoir (Delaware County)
  • West Branch Delaware River below Cannonsville Reservoir (Delaware County)
  • Mainstem Delaware River (Delaware and Sullivan Counties)
  • Esopus Creek downstream of the Shandaken Portal (Ulster County)

Upcoming Events

Catskill Mountainkeeper

Like us on facebook and be a part of our movement!