The concentration of egeria densa in Discovery Bay has been significantly reduced since the state’s intensive eradication program began in April, according to the Department of Boating and Waterways (DBW). But not all of the targeted areas have responded as well as expected, so treatment on the tenacious waterweed will continue for an additional few weeks.

“From what I understand, they are going to extend the treatment period and focus on some of those areas that have not responded as well to the applications,” said Discovery Bay General Manager Rick Howard. “It appears that the farther back into the bays they go, the more effective the treatment is. The closer they get to running water, such as near Indian Slough, it hasn’t worked as well.”

The original program, which began in April, was scheduled for 12 weeks, but the treatment will now continue for an additional four weeks in the two targeted locations. Area 1 is 192.2 acres and includes Marina, Shell, Sand and Cypress bays as well as Newport, Lighthouse and Beacon bays. Area 2 encompasses 76.9 acres and stretches from Lido Bay and Kellogg Creek to Cabrillo Bay.

“It is clear that the egeria densa is dying back throughout the bays and we fully expect it to continue dying back over the coming weeks and months,” said Chief Deputy Director Lucia Becerra in a June 29 report. “The symptoms we saw included translucent leaves, dark brown leaves and loss of the plant’s growing tip.

“However, some areas of Discovery Bay are showing the effects of the treatment less than others. This is due to several variables including water flows, water temperature, water depth, wind direction, initial amounts of egeria densa and area herbicide levels. Consequently, DBW will modify its treatment.”

DBW Public Information Officer Gloria Sandoval cautioned residents, prior to the commencement of the spraying, to give the slow-acting herbicide time to work and to avoid taking matters into their own hands by removing the weed themselves.

“It is critical to remember that it will take a few weeks to see any changes,” said Sandoval. “So we’re really urging people to leave the weeds alone and give the treatment time to do its job.”

But for some – especially those unable to navigate their boats out of their backyard bays because of the proliferation of the weeds – the temptation was too great. And now, said Becerra, there might be a financial penalty to pay.

“Harvesting the ergia will only exacerbate the problem,” said Becerra. “During our visit we spoke with harvesters who were using machetes to cut the egeria, and we are aware that certain residents have hired a mechanical harvester. The entire community of Discovery Bay will experience the effects of such treatments. The DBW has contacted USFWS (U.S. Fish and Wildlife Service), NOAA (National Oceanic and Atmospheric Administration) and CDFA (California Department of Food and Agriculture) for enforcement of laws on un-permitted harvesting, which adversely affects water, plants and wildlife.”

The egeria densa first grabbed the attention of Discovery Bay residents and officials last year when the unique combination of temperature, water and sunlight caused the fast-growing weed – most commonly found in pet stores and home aquariums – to expand its reach, clogging area bays and waterways up and down the Delta. But because treatment is so expensive – approximately $2,000 per acre – and requires a state permit, the herbicide was unavailable to the public.

Through a series of meetings hosted by Supervisor Mary Piepho, which included the DBW, Reclamation District 800 and members of Discovery Bay’s CSD, the state agreed to help.

“The Department of Boating and Waterways really stepped up and recognized the impact the egeria densa was having on the largest residential development in the Delta,” said CSD President Kevin Graves at the time. “I want to thank Supervisor Mary Piepho for bringing together all the governmental agencies to accomplish what we were originally told would never happen.”

The DBW’s treatment commitment – approximately $3 million – is for this year only, and when the project is completed, no additional DBW funding will be available.

“DBW will not be conducting this type of treatment in the future,” said Becerra. “This extensive effort was implemented to obtain control of the plant at this time … If DBW’s effort is successful this year, the subsequent treatment will be minor in comparison.”

Howard said the town is already considering alternative financial options: “They’re not coming back, so we’ll be working with our board, the county and Rec 800 to try and identify future resources. We’ve been very pleased with their involvement. DBW spent $3 million on this process, along with a quarter of their staff, and they’ve taken a very hands-on approach to Discovery Bay. We’re pleased they’ve acknowledged our problem. Now we’ll need to maintain it.”