Hydrilla: An Aggressive Water Weed

What's New

Herbicide Treatment in Fall Creek

August 14 fluridone pellets (Sonar One) were used in select locations in Fall Creek as planned. The endothall treatment was moderately successful; some small, isolated patches of hydrilla remain.

Cayuga Inlet and Fall Creek Post-endothall Monitoring

The level of herbicide in the water is monitored after each application until the herbicide is less than the detection limit.  View the laboratory results.  View the water monitoring protocol.

The Goal is Eradication

Hydrilla Eradication IS possible!  View map, summaries and full reports of successful hydrilla eradication efforts in California and Washington State. Also, check out the invasion curve, a graph displaying the importance of early detection and action.   


  • Is commonly known as hydrilla and water thyme.
  • Has been found in Cayuga Inlet (map of origional extent), Ithaca (August 2011).
  • Was found rooted in Cayuga Lake on August 21, 2013. Removal was finished August 30, 2013.
  • Is one of the world’s most invasive plants.
  • Can grow up to a foot a day.
  • Forms thick dense mats that block sunlight and kill native plants.
  • Reduces oxygen in the water and alters fish habitat.
  • Eliminates waterfowls feeding areas and fish spawning sites.
  • Obstructs boating, swimming, and fishing.
  • Lowers the value of waterfront property.
  • Blocks intakes at water treatment, power generation, and industrial facilities.
  • Clogs flood control channels.



Click on image for larger viewhydrilla

  • Hydrilla has pointed, bright green leaves about 5/8 inches long.
  • Leaves grow in whorls of 3 - 10 along the stem; 5 is most common. Leaves have small spines on the edges and at the tips, with a reddish center spine.
  • The most identifying characterists are the small, white to yellowish, potato-like tubers attached to the roots and the white floating flowers.
  • One-page update with hydrilla and look-a-likes (206 kb pdf).
  • The Cayuga Lake Watershed Network published an Invasive Weed Identification Guide in 2005 that covers dozens of invasive plants and the native plants they sometimes look like. (The image above was taken from this publication.)

Read more about hydrilla.

Last Updated: August 15, 2014

Last updated: August 15th 2014 - 11:21am