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Solving the Delta’s Invasive Aquatic Vegetation Problem

A recent science paper reminded me about the benefits of aquatic vegetation to lake fish species like largemouth bass. It also reminded me that invasive aquatic vegetation has ruined lake-like salmon habitats of the west coast, such as Seattle’s Lake Washington and portions of the Columbia River and California’s Bay-Delta estuaries. Instead of rearing salmon and smelt, these waters now rear non-native bass and sunfish (centrarchids). These once-turbid waters conducive to rearing juvenile salmon and smelt are now best suited for sight-feeding centrarchids, competitors and predators of salmon that love clear water and abundant cover. The non-native aquatic vegetation (Egeria, hyacinth, and milfoils) in the Bay-Delta provides abundant cover, uses all the aquatic plant nutrients, and collects the suspended sediment – all bad for the Bay-Delta’s pelagic/planktonic habitat.

Other than gripe about the obvious problem over the past several decades, what has anyone done about it? Boating and Waterways has tried spraying herbicides, but that has been costly, ineffective, messy, and organically/chemically polluting. Flushing the Delta all year with more-and-more clear reservoir water to south-Delta export pumps has not helped. The proliferation of non-native clams has also contributed to the problem.

There are no easy solutions, but there are options that should be implemented. Though costly and with their own environmental problems, these options can potentially lead toward recovery of the most important Delta habitats. The best option is an aggressive (and expensive) long-term program of manual cutting and harvesting using boat‐mounted cutters, harvesting barges, and suction dredges to remove the rooted and floating aquatic plants. A longer-term option is to increase turbidity from inorganic and organic sources by adding silts or reducing silt “sinks;” this would help cut sunlight and nutrients to rooted aquatic plants. Direct application of aquatic fertilizers has recently been considered by resource agencies; this could also help. Finally, reducing exports from the south Delta could help because it would reduce the proportion of low-turbidity reservoir water in the Delta and lessen the direct loss of millions of tons of silt.

Shifting the Bay-Delta habitat away from centrarchids by increasing Delta turbidity will measurably improve salmon and smelt recovery.