Aquatic Weed Update

  Following is an update on DBW’s egeria densa treatment at Discovery Bay…  (a letter from DBW).  Treatment Map below…

Last Thursday, June 23, DBW’s treatment team conducted a field visit. The treatment team included DBW’s environmental scientists and pesticide manager, the State’s federal nexus with the US Agricultural Research Service who is a noted expert in ergeria densa and other invasive plants control, an herbicide biologist with SEPRO Corporation, and myself.

During this trip we visited all of Discovery Bay, carefully examined egeria plants in all parts of the Bay, and took plant and water samples. In addition, we met with a Discovery Bay resident who went over in detail what his experience has been with the egeria this season. We walked his dock and a neighbor’s dock.

Based on all of the scientific data that DBW has collected during the course of treatment (which includes more sampling that any other control project that we can find) and our extensive work on Thursday, we found the following. It is clear that the egeria densa is dying back throughout the Bay, and we fully expect it to continue dying back over the coming weeks and months. The symptoms we saw included translucent leaves, dark brown leaves, loss of plant growing tip, loss of leaves, floating plants (which had not been cut by a harvester), and egeria densa canopies which have dropped (sinking).

However, some areas of Discovery Bay are showing the effects of 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 has modified it’s treatment. DBW now plans to treat all areas of areas 1 and 2 for 16 weeks, and to increase treatment levels for the areas which have not progressed to the same extent as others.

DBW will continue to conduct its treatment in full compliance with it’s federal and state law. As you are aware, treating Discovery Bay requires some very difficult balancing because the adjacent agricultural lands receive irrigation water from Discovery Bay. Other Invasive plants. Currently, many aquatic plants exist in Discovery Bay. Bright green fillamentous algae is currently floating on the water in many areas in Discovery Bay. It is not egeria densa. This algae should float away or dissipate when the egeria drops. DBW as asked the federal government for permission to treat this algae; however, no approval as been received at this time. Large mats of pennywort are also floating in Discovery Bay. They will likely float away. Several other types of algae and plants were also seen on the team’s visit.

Short-Term Versus Long-Term:   As you are aware Discovery Bay has experienced many years of egeria densa infestation. DBW’s treatment this year is the best solution for addressing the problem in 2011. Any belief that the treatment is not working is not based on scientific or observational evidence. Harvesting the egeria will only exacerbate the problem. 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. DBW has contacted the enforcement arms of USFWS, NOAA, and CDFA for enforcement of laws on unpermitted harvesting which adversely affects water, plants, and wildlife. Please note that DBW will not be conducting this type of treatment in the future. This extensive effort ($3 -$6 million) was implemented to obtain control of the plant at this time. However; the local entities, such as Discovery Bay and County, will be responsible for developing a comprehensive vegetative management plan and carrying out treatment in the future. If DBW’s effort is successful this year, the subsequent treatments will be minor in comparison. DBW’s role in the future will be primarily to provide technical assistance and supplemental application assistance to the County and community. D

BW strongly urges the community to maintain patience and consider short-term v. long-term benefits. DBW thanks the community for all of the updates, information, and suggestions. With respect to the safety issues you have raised, DBW will contact the Contra Costa Sherriff. Please contact me if you would like to discuss.

Lucia C. Becerra Chief Deputy Director / Acting Director

Department of Boating & Waterways

 lbecerra@dbw.ca.gov

FOR TREATMENT AREA MAP:  

FOR MORE DETAILS, VISIT THE TOWN OF DISCOVERY BAY WEB SITE:  http://www.townofdiscoverybay.org/content/delta-weeds/