ILWACO — It’s back.
Not as bad as it was years ago, when the Ilwaco residents really began to see it as a problem, growing thick and happy right under the surface of Black Lake, but still...
“It’s fairly substantial,” said Jeff Nesbitt, director for Pacific County’s Vegetation Management department.
The non-native, invasive aquatic weed Brazilian Elodea has flourished this year in Black Lake, harried not by the introduction of sterile grass carp — one solution the city experimented with in the late 90s; the fish were supposed to nibble away at the plants and control them the way flocks of sheep keep the grass short in fields — nor by the frequent spraying of herbicides. The last time the lake was sprayed was last spring; according to the city, the lake should be treated at least three times a year.
The lake is due to be treated this fall, but application of the herbicide diquat will have to wait until after the cranberry harvest.
“The plant doesn’t necessarily work on the same schedule as the cranberry farmers,” Nisbett said.
City officials in Ilwaco — and in Long Beach in regards to Loomis Lake — fear that Brazilian Elodea could choke out other plant life in the lake.
In February, the city of Ilwaco received an extension for an aquatic weed grant from the Department of Ecology, allowing the grant to continue into June 2017. This grant has funded more recent control efforts. Roughly $57,000 of the grant funds remains. The city had originally requested and received $75,000 in grant funds from DOE’s Water Quality Program, Aquatic Weeds Management Fund.
In the past, the Ilwaco Parks and Recreation Commission had organized spraying of the lake, but at a council meeting in February, Councilmember Vinessa Karnofski said the commission did not have the time to do this. Since DOE was willing to extend the grant, the city was able to contract with Pacific County’s Department of Vegetation Management.
The herbicide Nesbitt plans to use, diquat, has been used in the United States to control crops and aquatic weeds since the 1950s. According to the EPA, it can cause cataracts in people if they drink water containing the herbicide in excess of the maximum contaminant level for many years. The EPA’s threshold for diquat is 20 parts per billion.
The city and county are not concerned, and the treatment should be a straightforward process, Nesbitt said. The label for the herbicide is very clear about how much should be used depending on the volume of water, weather conditions, and water flow through the area.
Since the summer has been so dry, the volume of Black Lake is fairly easily to calculate. The lake is normally fed by precipitation and groundwater, while the surface water drains out along a channel at the north end into Tarlett Slough and Willapa Bay. This summer, the drainage channel is basically dry dirt and mud, which means the volume in the lake is relatively stable. Nisbett likely won’t have to calculate flow out into the bay.
Treating Black Lake will still be a bit of a balancing act, though. Local cranberry farmers, the McPhail family whose farm is located to one side of the lake, hold water rights to the lake and can draw on it to fill their cranberry bogs at harvest time.
Ideally, Nisbett would treat the plants during in the two major flushes of growth in the spring and summer. For now, his goal is to hit the plants right after the cranberry harvest is done this fall.
Nisbett anticipates it will take only a few days to completely treat the lake. After treatment, the water should be avoided for three to five days.
“In terms of waiting period that’s extremely short,” Nisbett said.
The herbicide will not completely eradicate the weeds. The roots remain alive, and the plants will grow back. As part of its contract with the city of Ilwaco, Pacific County will monitor the lake after treating it and conduct several surveys.
According to a survey of Black Lake published in January 2000 by the Washington Department of Fish and Wildlife’s Warmwater Enhancement Program, “A diverse, thriving aquatic plant community is essential for the well-being of many warmwater fish species, which are more likely to be found in areas with aquatic plants than in areas without them.”
Black Lake supports several fish species and is stocked with rainbow trout — most recently in May — and the city holds a fishing derby there.
“Submersed aquatic vegetation provides important foraging, refuge, and spawning habitat, improving survival and recruitment to harvestable sizes,” the survey from 2000 continues. “For these reasons, it is important to gather baseline information and carefully review all proposals to limit or control aquatic vegetation for a given lake, especially when the lake supports a popular fishery.”