Starting March 20, the Division of Boating and Waterways will begin herbicide treatments. Photo  courtesy of California State Parks’ Division of Boating and Waterways

SACRAMENTO, CA (MPG) – California State Parks’ Division of Boating and Waterways (DBW) began its 2025 control efforts for invasive aquatic plants in the Sacramento-San Joaquin Delta and its southern tributaries (Delta) this month.

Starting March 20, after press time, the Division of Boating and Waterways began herbicide treatments on water hyacinth, South American spongeplant, Uruguay water primrose, alligator weed, Brazilian waterweed, curlyleaf pondweed, Eurasian watermilfoil, coontail, fanwort, and ribbon weed in the Delta. The treatment start date can change, depending on weather conditions and plant growth/movement.

“DBW continues to work with the public and our local, state and federal partners to control these aquatic invasive plants to reduce or eliminate the negative impacts on people’s daily lives and businesses,” said Division of Boating and Waterways’ Deputy Director Ramona Fernandez. “The continued use of monitoring and technology allows the division to focus on the areas that best help us manage the challenges.”

These aquatic invasive plants have no known natural controls in the Delta, the West Coast’s largest estuary. They negatively affect the Delta’s ecosystem as they displace native plants that are essential to the area’s biodiversity while negatively impacting the economy, environment and public health. Continued warm temperatures help the plants proliferate at high rates.

The plants are also known to form dense mats of vegetation, creating safety hazards for boaters and obstructing navigation channels, marinas and irrigation systems. Due to their ability to spread rapidly to new areas, the plants will likely never be eradicated from Delta waters. Therefore, Division of Boating and Waterways operates control programs as opposed to eradication programs. The division works with local, state and federal entities to better understand the plants and implement new integrated control strategies to increase efficacy. 

Funding for Division of Boating and Waterways’ aquatic invasive plant control programs comes from the Harbors and Watercraft Revolving Fund, which receives revenues from boaters’ registration fees and gasoline taxes.

All herbicides are registered for aquatic use with the U.S. Environmental Protection Agency and the California Department of Pesticide Regulation. Treated areas for submersed aquatic vegetation (Brazilian waterweed, curlyleaf pondweed, Eurasian watermilfoil, coontail, fanwort, and ribbon weed) will be monitored to ensure herbicide levels do not exceed allowable limits and follow EPA-registered label guidelines. The public can view the public notices and sign up to receive weekly updates on this year’s treatment season at the Division of Boating and Waterways’ website at dbw.parks.ca.gov.

Below is a list of proposed area control actions for the 2025 treatment season.

Floating Aquatic Vegetation Control Program is to control water hyacinth, South American spongeplant, Uruguay water primrose and alligator weed. Herbicide control treatment period is for all sites from March 20 to Nov. 30. Types of herbicides are Glyphosate, Imazamox, 2,4-D or Diquat.

Potential treatment areas are initially in and/or around but not limited to the following areas: San Joaquin River, Old River, Middle River, Fourteen Mile Slough and Snodgrass Slough.

The submersed Aquatic Vegetation Control Program is to control Brazilian waterweed, curlyleaf pondweed, Eurasian watermilfoil, coontail, ribbon weed, and fanwort. The herbicide control treatment period from March 20 through Nov. 30, based upon Division of Boating and Waterways field survey data, water temperatures and fish surveys, uses Fluridone, Diquat or Endothall herbicide. Potential Sacramento-area treatments will be at French Island, Hogback, Long Island Slough, Sacramento Marina, Snug Harbor and Washington Lake.

Last year, Division of Boating and Waterways treated a total of 2,649 acres of floating aquatic vegetation and 1,115 acres of submersed aquatic vegetation. No mechanical harvesting was conducted. A combination of herbicide, biological and mechanical control methods will be used to help control invasive plants at high-priority sites in the Delta.

In 1982, California state legislation designated Division of Boating and Waterways as the lead state agency to work with other state, local and federal agencies in controlling water hyacinth in the Delta, its tributaries and the Suisun Marsh. The Egeria Densa Control Program was authorized by law in 1997 and treatment began in 2001. In 2012, spongeplant was authorized for control upon completion of the biological assessment. In 2013, Division of Boating and Waterways’s jurisdiction expanded to include other invasive aquatic plants, and since then, other aquatic invasive plants such as Uruguay water primrose, Eurasian watermilfoil, Carolina fanwort, coontail, alligator weed and ribbon weed have been added to the Aquatic Invasion  Plant Control Program.

To report sightings, subscribe for program updates or for more information regarding the control program, connect online at dbw.parks.ca.gov/AIS, email at AIS@parks.ca.gov or phone at 888-326-2822.