If you have appreciation for water, chances are you rejoiced at the sight of our county’s percolation ponds beginning to fill earlier this spring. A much anticipated El Niño winter season left our local and state reservoirs fuller than they’ve been in the last three years. More water in California’s reservoirs and snowmelt from the Sierra snowpack resulted in a much improved allocation of imported water that comes through the Sacramento-San Joaquin Delta. This means that we, the Santa Clara Valley Water District, have been able to send water to our percolation ponds to replenish our groundwater supplies, which have been depleted during the drought.

So, where is this water now, you may ask? Since mid-July, you may have noticed water levels drop in some of the percolation ponds throughout the county. There are a few reasons for the recent decrease which include reduced water releases, low water levels in San Luis Reservoir, algal blooms and groomed ponds. The story starts with the endangered Chinook salmon in the Sacramento River.

State and federal agencies regulate water releases from reservoirs to streams and rivers to protect fish. Federal officials have reduced the release of water from the state’s largest reservoir, Lake Shasta, to help Chinook salmon later in the year, even though the reservoir nearly filled this year. The salmon need cold water in the fall, and fishery agencies are concerned that releasing water from Shasta now would mean water released this fall would be too warm for the salmon. Cold water is trapped deep in the reservoir. Releasing too much water now will deplete the pool of cold water, leaving shallower water levels that will warm up faster in the sun.

Water from Lake Shasta flows down the Sacramento River and through the Delta where some of it is stored in other reservoirs, like San Luis Reservoir. Water is normally pumped into San Luis during the winter season, and drawn from the reservoir during the summer and fall months. However, last winter, fishery agencies restricted the amount of water pumped into San Luis to protect fish in the Delta. The restricted pumping in addition to the need to keep cold water in Shasta for salmon later in the year, has resulted in storage levels in San Luis Reservoir that are critically low, and our county’s water quality and water supply reliability are being challenged.

Low water levels and warm temperatures are perfect breeding ground for algae, which can cause taste and odor issues in our drinking water. Currently, algae in San Luis is causing the water to have an earthy, musty taste and odor. The water district has been working to improve the taste and odor in drinking water. However, the lower the water level drops in San Luis, the more pungent the issue may become and we may not be able to use water from the reservoir.

We also import water from the South Bay Aqueduct which carries water pumped up from the Delta to our county. This summer, the Delta has also experienced algal blooms, so we have had to limit the amount of Delta water we can use at our treatment plants.

Normally, we use imported water, in addition to local water, in the summer to supply our percolation ponds. Because of the algae problems, we have had to also limit the amount of imported water entering our system. The only other viable alternative has been water from Anderson and Coyote reservoirs. That’s enough water to supply our water treatment plants, but not enough to also keep the percolation ponds replenished.

Early last week, we had to resort to these local water sources to combat taste and odor issues from imported water sources. Even though the water may have an unpleasant taste and odor, it is still safe to drink and does not pose any health concerns. Residents can chill tap water before drinking to improve the smell and taste.

Another reason the water is dropping at our groundwater recharge ponds is that the rate of percolation, or the rate at which the water seeps into our groundwater aquifers, has doubled, or in some cases tripled, due to a thorough cleaning and grooming effort two years ago. In the last two years the drought left many ponds completely empty. During that time our crews worked diligently to remove plenty of vegetation and sediment, and as result the water is now percolating faster and more efficiently.

While the water district works to minimize the taste and odor issues, the Los Alamitos Guadalupe McGlincy ponds in South San José have begun waning. In the next few weeks you can expect water levels in the Kirk and Page pond systems in Campbell to decrease dramatically as well. Unfortunately, our groundwater recharge program will have to be scaled back until imported water conditions improve.

Although it will take some time to improve the reliability and quality of our imported water supplies, the water district is evaluating other long-term projects. The state has asserted that the California Water Fix project will improve the transfer of water across the state while reducing environmental threats to fish. The water district is evaluating the proposed project to analyze the potential benefits for our county’s future water supply.

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