Hydrilla: An Aggressive Water Weed

2013 Plant Monitoring Report

Summary of the 2013 aquatic plant results from the monitoring surveys in the Cayuga Inlet and the south end of Cayuga Lake includes  evaluation of the densities of subterranean hydrilla turions (tubers) in the sediments of the infested areas. Full report, 2013 Monitoring Report of the Cayuga Inlet and Southern Cayuga Lake Monoecious Hydrilla Eradication Project  includes maps and data.

2013 Hydrilla Season Is Complete

The Fall Creek endothall treatment and the Cayuga Inlet endothall and fluridone treatments have been completed, as well as water monitoring for Fall Creek and the Cayuga Inlet. The patches of hydrilla found in the southeast end of Cayuga Lake have been removed and are now being covered with benthic barriers. The endothall treatment to Fall Creek was successful in inhibiting further tuber growth and pushing back hydrilla growth. Cayuga Inlet endothall and fluridone treatments have been very successful, showing a decrease in tubers from an average of 304 tubers per square meter in 2011 down to 5 tubers per square meter. View a complete overview of the 2013 Hydrilla Eradication Efforts.

Cayuga Inlet Fluridone Monitoring Completed December 2

The herbicide fluridone (trade name: Sonar One/Sonar Genesis) was applied to the Cayuga Inlet treatment area between August 14 and October 15. Water monitoring of fluridone concentrations was conducted within and outside of the treatment area 24, 48, and 72 hours, and weekly once the treatment began. Fluridone concentrations dropped below 1 ppb (the safe level at which water can be used for irrigation of all plants) at all sites except one by October 21. Levels remained elevated at site 8 (Robert H. Treman Marina) due to the Sonar One "bump" application done on September 16. The level of fluridone at site 8 dropped below 1 ppb on December 2. Accoridng to TCHD and NYSDEC monitoring protocol, fluridone monitoring results for the Cayuga Inlet are now complete. Herbicide warning signage for fluridone have been removed. View more information about the herbicide application and monitoring in the Cayuga Inlet. 

Hydrilla Found in Cayuga Lake

On August 21, 2013, while conducting extensive surveys in the southern end of Cayuga Lake, survey crews  discovered small patches of hydrilla growing in the south east corner of Cayuga Lake (dots within yellow circle). Click on map for larger view. 

Each patch is probably the result of a single tuber. The survey crew found the patches of hydrilla while conducting an extensive rake-toss survey after hydrilla was found in Fall Creek on August 8. Read more about the first hydrilla found growing in Cayuga Lake.  


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: March 13, 2014

Last updated: March 13th 2014 - 10:07pm