A lot of the concepts and issues we’ve discussed in this series require complex thinking and solutions. Even our last issue, Ecosystem-wide Management: Bold Action #1, requires significant adjustments in how water managers think about the Delta. However, bold action No. 2 should be low-hanging fruit for the next administration to pick – controlling harmful invasive species.

It is widely known that the Delta is teeming with more than 185 invasive species, ranging from aquatic plants to sport fish to nasty beaver-like varmints known as Nutria. In fact, it is estimated that at least 95 percent of the aquatic biomass in the estuary is non-native and these unwelcome guests continue to be among the most serious stressors on the ecosystem. Addressing the harmful impacts of invasive species must become a priority. And yes, it is difficult and expensive – which might explain why little work to really understand how they alter the ecosystem has been conducted and efforts to control them have been so limited.

“Taken together, the large number of exotic species, their dominance in many habitats, and the rapid and accelerating rate of invasion suggest that the San Francisco Bay and Delta may be the most invaded estuary and possibly the most invaded aquatic ecosystem in the world.

– Andrew N. Cohen and James T. Carlton, Accelerating Invasion Rate in a Highly Invaded Estuary

One prime example of how invasive species are taking over, and wreaking havoc is the prolific water hyacinth. Recent reports have indicated that the ornamental plant has approximately doubled over the past ten years and increased more than 50 percent over last year, choking out as much as a third of the Delta’s 60,000-acres of water ways.  The plant can double in size every ten days in warm weather conditions, becoming up to six feet thick. This dense vegetative mat exacerbates conditions favoring other invasive species by reducing turbidity in which delta smelt can hide and providing cover for non-native predators who prefer warmer, stagnant water. In addition, hyacinth consumes water, depletes oxygen, clogs waterways, and limits biological diversity of important organisms that are a vital food source for native endangered species.

A more recent intruder, Nutria, has the potential to create catastrophic harm to the Delta levee system and damage the ecosystem. The 20-pound rodent is able to devour as much as a quarter of their body weight in vegetation each day, wasting and destroying as much as ten times that amount. These destructive feeding habits cause extensive damage to native plants and destroy marshlands resulting in further loss of critical habitat and wetlands, necessary for native species. Nutria are prolific breeders and are difficult to detect. The potential for breaching levees and the flooding of delta islands and resulting severe water supply disruptions for Bay Area and Southern California residents and Central Valley farms demands an aggressive eradication effort.

While millions of dollars have already been spent on efforts to reduce the impacts of these and other non-native pests, it hasn’t been enough. And more invasive species will continue to arrive. Managing the ecosystem to encourage native and deter invasive species in the Delta is not a controversial action and is one that could provide the next Governor a significant and important contribution to Delta management. If the next Governor is serious about rehabilitating the Delta and its native salmon species, he must allocate some serious resources to better understand and control the problem of harmful invasive species.

water hyacinth harvest