The fate of a national treasure and several endangered species is in the hands of a small local water district: Fish Slough. Groundwater pumping in the Tri-Valley basin to the north is impacting the water table in Fish Slough. You would think the new California Sustainable Groundwater Management Act (SGMA), meant to ensure underground aquifers aren’t lowered to the point that groundwater-dependent ecosystems suffer, would save this important habitat, but it won’t. Only the actions of ranchers, farmers, and residents in the Tri-Valley water district can save Fish Slough.
Fish Slough is in Mono County to the north of Bishop, CA. The flat valley floor lies between the Volcanic Tablelands to the west and a ridge of low buttes to the east. In the spring, this slough turns green and is alive with birds, bees, butterflies, and other wildlife. In winter it turns golden with lacy-top reeds interspersed with patches of rust-colored marsh marigolds. Many endangered and sensitive species live there: Fish Slough springsnails, Fish Slough milk-vetch, Silverleaf milk-vetch, Hot Springs fimbristylis, Alkali ivesia, Inyo phacelia, Inyo star tulip, and Owens Valley checkerbloom.
Perhaps the slough is best known as the home of the endangered Owens Pupfish. The tiny, 2-inch male fish turn bright blue during spawning and the cream-colored females observe their brawls. This ancient species had persisted in the Owens Valley from Fish Slough to Lone Pine since the ice ages. But with habitat loss, the drying of the Owens River, and the illegal introduction of its predators, including non-native bass and mosquito fish, the pupfish’s range shrank and the species almost perished entirely. (Photo credit left: L. Boulton)
Fish Slough became the pupfish’s last remaining natural habitat. They did well in the slough’s shallow springs and slow-moving streams. But by 1969 there was only one area left with pupfish, and it was drying. Fish biologist Phil Pister scooped hundreds of pupfish up in two buckets and transported them to safety. (Photo credit right: C. Bubser)
Since then, the pupfish have been re-established in the slough. However, groundwater flows in Fish Slough have been in decline for the past 20 years and once again threaten the survival of the Owens River Pupfish (see graph below). In response, California Department of Fish and Wildlife (CDFW) biologists have been translocating the pupfish to new locations, but 90% of the translocations have failed for various reasons. The springs in Fish Slough are dependent upon upward pressure of water from the deeper aquifer. If the drop in the water table continues, it will affect the springs. Eventually, remaining pupfish populations in Fish Slough will die.
Interestingly, the 1998 US Fish and Wildlife Services (USFWS) Owens Basin Wetland and Aquatic Species Recovery Plan referring to the Owens Pupfish states, “Actions should be taken to protect [spring] discharge at 1998 levels.” (Task 2.1.6 Protect Spring Discharge). USFWS wanted to hold the line at that level back then. Unless a basin is monitored and managed, a recovery goal like this cannot be met.
There are two key reports that show that the water flowing through Fish Slough comes from the Volcanic Tablelands and the Tri-Valley. The groundwater flows from the Benton Range and White Mountains to the north, south towards Bishop. When it gets to Chalfant, it is shunted west around a block of bedrock to Fish Slough. Very little flows directly south to Laws in Inyo County.
Through the Owens Valley Groundwater Authority (OVGA) Groundwater Sustainability Plan (GSP) preparation process, it was discovered that the Tri-Valley is a sub-basin of some concern. The OVGA GSP reports that Tri-Valley’s groundwater pumping is impacting Fish Slough. The hydrographs of the monitoring wells in Fish Slough show the decline in the water table. There is no groundwater pumping in the Tablelands, but there is in the Tri-Valley. The OVGA GSP also identified data gaps related to Tri-Valley that would need to be filled. More monitoring wells are needed as is a modeling tool that would project how much groundwater pumping in the Tri-Valley could occur without impacting Fish Slough. To protect Fish Slough and the unique pupfish it sustains, it is critical to fill these data gaps.
The Los Angeles Department of Water and Power (LADWP) owns most of Fish Slough waterway and the Owens Valley to the south of it. So, when the groundwater flows into Fish Slough, it becomes LADWP’s water. LADWP doesn’t have production wells in Fish Slough or near it, but as we all know, it is in the business of exporting water. That places Fish Slough in the middle between LADWP’s thirst for water and the water needs of the Tri-Valley's ranchers, farmers, and other residents. If Tri-Valley users take all of the groundwater for themselves in order to keep it out of the hands of LADWP, then little or no water will flow through Fish Slough and it will dry up. Tri-Valley water users have to let an adequate amount of groundwater flow through Fish Slough even if it feeds the aquifer that LADWP can tap. That’s a big ask. Use it or lose it to Los Angeles is a common mind-set. (Photo credit: L. Boulton)
The Tri-Valley sub-basin is in Mono County, but it is part of the Owens Valley watershed, so it was included in the Owens Valley Groundwater Sustainability Plan (GSP) that was recently submitted to the state Department of Water Resources. In January 2022, Mono County decided to withdraw from the Owens Valley Groundwater Authority (OVGA) because all the other agencies in it were in Inyo County. Mono County didn’t want to be part of a structure that would allow Inyo County to manage groundwater in Mono County. But by not participating in how water is used in the Tri-Valley, Mono County has effectively sold the Owens Pupfish down the river.
The SGMA has rated Tri-Valley a low priority sub-basin of the Owens Basin. As a low priority sub-basin, a sustainability plan is not required and groundwater management is voluntary for now. The Tri-Valley Groundwater Management District (GMD) plans to develop their own groundwater sustainability plan. However, it will take several years before a GSP will be in place. Now that Mono County has withdrawn from the OVGA, it isn’t clear when the data gaps will be filled and who will pay to address them, once the GSP is developed.
Fish Slough, and the important species it supports, are extremely vulnerable. There's no doubt about that. It is now up to the Tri-Valley GMD to save Fish Slough and the pupfish. What is in doubt is if they will and if it will be in time. If you are interested in what comes next, you can attend the Tri-Valley GMD board meetings on the 4th Wednesday of every month at 6:30pm. If you cannot, please let them know how important Fish Slough is to you and encourage them to act quickly. Instructions are on the TVGMD.org website. Copy the Mono County 2nd District Supervisor, Rhonda Duggan, as well.
You can also write to the CA Department of Water Resources at sgmps@water.ca.gov and encourage them to rate the Tri-Valley sub-basin a medium priority immediately; not in 2025 with the next cycle of re-rankings. A medium priority groundwater basin requires a groundwater sustainability plan within a certain timeframe.
Lynn Boulton
A great article on Fish Slough: https://www.nytimes.com/2021/08/16/science/owens-pupfish-pister.html