In the Feb. 11, 2015, photo above, waters are extremely low in Lake Success near East Porterville, California, in the San Joaquin Valley. Excessive pumping of groundwater has caused the area to slowly sink since the 1920s.

(David McNew/Getty Images)

Excessive pumping of groundwater from California’s San Joaquin Valley has caused the area to slowly sink since the 1920s and has raised concerns that underground aquifers will be affected, according to a recent report from NASA.

, NASA says.Prolonged periods of drought have worsened the subsidence, as farmers rely heavily on the groundwater to maintain one of the nation’s most productive agricultural regions.

“,” California Department of Water Resources Director William Croyle said in a release on the report. “Subsidence has long plagued certain regions of California. But the current rates jeopardize infrastructure serving millions of people. Groundwater pumping now puts at risk the very system that brings water to the San Joaquin Valley. The situation is untenable.”

Long-term subsidence has already damaged thousands of public and private groundwater wells throughout the area. Additionally, it can reduce the amount of water underground aquifers can hold and threaten future water supplies. Federal water agencies have spent an estimated $100 million on repairing subsidence-related damages since the 1960s, according to the release.

that open up on the land surface, according to the Oilfield Review. These bowls are caused by the pressure used to drive fluids up from reservoirs, which degrades surface soil and can cause increased erosion.

The satellite image above shows total subsidence in California’s San Joaquin Valley between May 7, 2015, and Sept. 10, 2016. Two large subsidence bowls are evident, centered on Corcoran and southeast of El Nido, with a small, new feature between them, near Tranquility.

(European Space Agency/NASA-JPL/Caltech/Google Earth)

Between May 2015 and September 2016, two bowls found near the towns of Chowchilla and Corcoran cover hundreds of square miles and continued to grow deeper and wider, according to the report. The Corcoran bowl saw sinkage of almost 2 feet and the bowl in Chowchilla sunk about 16 inches. The subsidence has affected aqueducts and flood control structures.

“If you see a subsidence bowl, then something is going on at the center of the bowl that is causing the land to sink,” report co-author Cathleen Jones said in the release. “For example, high levels of groundwater pumping.”

Using multiple satellites and radar imagery, the NASA JPL scientists were able to obtain subsidence measurements from images of Earth’s surface. Some of the images were acquired as early as 2006.

“We can locate problem spots so the state can focus on those areas, saving money and resources,” said Jones. “We find the needle in the haystack, so to speak.”

The scientists discovered that the California Aqueduct, which supplies 25 million residents and nearly a million acres of farmland with water, is being directly impacted by localized subsidence.

The satellite image above shows the relative expansion of a subsidence bowl centered just north of a road in Avenal, California, and just east of the California Aqueduct between March 2015 (left) and June 2016 (right). Only areas subsiding more than 10 inches are plotted. About 5 miles of the aqueduct has been lowered by more than 10 inches.

(NASA/JPL-Caltech/ESRI)

The system of canals, pipelines and tunnels carries water 444 miles from the Sierra Nevada and Northern and Central California valleys to Southern California. Maximum sinkage near the aqueduct has reached 25 inches near Avenal in Kings County, according to the report.

Since the initial construction of the aqueduct, subsidence has caused a reduced flow of only 6,650 cubic feet per second, which is 20 percent less than its designed capacity of 8,350 cubic feet per second, states the release. In order to avoid overtopping the structure’s concrete banks, water project operators have to reduce flows in the sunken sections.

The California Department of Water Resources (DWR) is analyzing whether the dip in the aqueduct will affect deliveries to water districts in Kern County and Southern California. If the area’s allocation of water is 85 percent or greater, delivery may be hindered this year due to impacts from the sinking land in the Avenal-Kettleman City area.

The data also found subsidence of up to 22 inches along the Delta-Mendota Canal, a major artery of the Central Valley Project. The project supplies water to approximately three million acres of farmland and more than two million Californians.

The Eastside Bypass, which is designed to carry flood flow offof the San Joaquin River in Fresno County, runs through an area of subsidence in which the land surface has dropped between 16 and 20 inches since May 2015, also according to the release. This is on top of several feet of depression measured between 2008 and 2012.

In 2000, a five-mile stretch of the bypass was raised because of subsidence and DWR estimates it may cost about $250 million to establish flowage easements and levee improvements to restore the design capacity of the sunken area.

DWR has been working with local water districts to determine if surface deformation will interfere with flood-fighting efforts, especially as a heavy Sierra snowpack melts this spring.

Though the NASA researchers discovered a few eye-opening developments in the sinking valley, they also found that subsidence in the valley slowed during the winter of 2015-16 when rainfall amounts were enough to water their crops, according to the release.

“While we can see the effect that rain has on subsidence, we know that we’ve run a groundwater deficit for some time, so it’ll take a long time to refill those reservoirs,” said report co-author Tom Farr.