Treatment began this week to curb a pair of invasive aquatic weeds in the Delta waters around eastern Contra Costa County.

But the state Division of Boating and Waterways' list for Egeria densa control does not include Discovery Bay's waterways, which in summers past have been carpeted with the plant.

Contra Costa areas included as part of the 2,119 acres of Egeria densa treatment are Franks Tract near Bethel Island and the Clifton Court Forebay area by Old River. Other locations that will receive the Fluridone treatment are boat ramps and marinas in Isleton, Stockton and Sacramento.

The state agency's work to control water hyacinth also shifted this week to the south Delta area, including the waters near Pittsburg, Antioch and Oakley.

Gary Loretz pulls out a handful of Egeria densa from his backyard dock in Discovery Bay. (Sherry LaVars/Staff Archives)
Gary Loretz pulls out a handful of Egeria densa from his backyard dock in Discovery Bay. (Sherry LaVars/Staff Archives)

The state is spending about $3.15 million on the 12 weeks of Egeria densa treatment, which is funded by boater registration and gas taxes. The price tag for water hyacinth treatment, which runs through November, is about $200,000.

The state is working on environmental documents to treat a third aquatic weed identified in the Delta, the South American spongeplant.

Invasive vegetation can crowd out native plants, slow water flows, block off oxygen to fish and clog water intakes. It is unknown whether this year's severe drought has affected the growth of Egeria densa in the Delta, but department spokeswoman Gloria Sandoval said the agency continues to monitor the situation.


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Egeria densa, often found in aquariums, is at a manageable level in Discovery Bay and does not clog waterways to the point where boaters can't maneuver, according to the state.

"If (Egeria densa) were at those levels at any another area of the Delta, we would not be treating there," Sandoval said.

County Supervisor Mary Nejedly Piepho, of Discovery Bay, said being off the treatment list came as a surprise, given the collaborative work with the department the past three years.

"It's sort of a good news, bad news," Piepho said. "It has been so effective, and the Egeria densa is not nearly at the level it was before. But we don't want to go backward."

Her office sent a letter to the state asking officials to reconsider.

With the additional space in Discovery Bay waters, a new invader has emerged.

Curly-leaf pondweed, a flat-stemmed plant with thick, wavy leaves, now covers about 70 percent of the water, said Jeff Conway, manager of the local reclamation and drainage maintenance district. Egeria densa still accounts for 20 percent of the plants in the water.

The good news for boaters is that the pondweed blossoms in late winter months and should die down in about a month, Conway said.

Piepho said a meeting will soon be held with various stakeholders, including local lawmakers, the Delta Stewardship Council, Delta Conservancy, U.S. Department of Agriculture and Boating and Waterways, to discuss Delta-wide aquatic weed-management efforts.

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.

What Can You Do?
Officials with Reclamation District 800 in Discovery Bay offer these tips to pull and properly dispose of aquatic plants.
  • Pull the plants and weeds from their roots. Remove the entire plant/weed, including the roots.
  • Place the entire plant in garbage bags or cans and move them far away from the water. If they are left to dry on the dock or near the water line, seeds will blow back into the water and cause more growth.
  • Encourage your friends and neighbors to properly remove and dispose of aquatic plants near their property.
  • Avoid any contamination of the waterways. All spraying must be done by a licensed pesticide applicator. This is required under the Clean Water and Endangered Species Acts. 
    For more information on the treatment, visit www.dbw.ca.gov/AquaticInvasiveSpecies.