First Nations people in northern California are fighting to save the environment and their communities from ranchers who are defying state orders to reduce their water usage.

The ranchers, operating under the banner of the Shasta River Water Association, have diverted flow from the Shasta River, putting the salmon population of the Klamath tributaries at risk.

Yurok and Karuk tribes say the diversion caused a 37 per cent decrease in Shasta River flows in just two hours on August 17.

First Nations leaders noted that just days before the diversion, thousands of fish were killed by a mudslide caused by wild fires devastating the vegetation that stabilised the soil.

In a statement issued last Tuesday, Karuk chairman Russell Attebery said the rangers were breaking the law by dewatering one of the most important salmon nurseries in California.

"After last week's fish kill, every juvenile salmon in the Klamath basin must be protected to ensure future runs. We are horrified, we are angry, and we expect accountability," he said.

In June last year it was reported that the Shasta River flows had been drastically reduced by drought and agricultural use.

The Shasta River Water Association delivers irrigation to small ranches and farms.

In August 2021 California's State Water Resource Control Board imposed a water reduction order on residents of the Shasta and Scott River valleys in Siskiyou County after the state's governor, Gavin Newsom, declared a drought emergency.

Karuk senior fisheries biologist Toz Soto said the water reduction order would maintain minimum flows in two of the Klamath's most productive tributaries for Chinook salmon.

"These flows reflect the best available science and are the minimum amount of water the fish need to survive in drought years," he said.

The two rivers have long been home for salmon to spawn and lay eggs before returning to the ocean.

On the day of diverting Shasta River, the Shasta River Water Association told the Division of Water Rights their plan to defy the water reduction order.

Courthouse News Service reported that in a letter to the division's deputy director Erik Ekdahl, the Association said it would follow exemptions in the order by curtailing the river 15 per cent and pumping to supply water to livestock "as the weather is over 90 degrees (32.2C)".

"We will also follow the suggestion to fill ponds for fire suppression and attempt to water the tree base to reduce fire hazards to the community and our families," the letter said.

"At this time, we are choosing to protect the health of livestock, wildlife and families."

The State Water Resources Control Board issued a cease-and-desist order in response, arguing the Association's water rights were amended under the emergency drought regulation.

The ranchers could face fines of up to US$10,000 per day if they persist.

The Yurok and Karuk tribes are exploring their legal options for holding the Association accountable for diverting the river.

Karuk natural resources consultant Craig Tucker told Courthouse News that the ranchers are stealing water from the rest of California.

"They're killing fish that are protected to the benefit of California fishermen and for tribes," he said.

"If these guys get away with it here, next thing you know, farmers and ranchers are just going to ignore state agencies and federal agencies when they try to regulate."

Yurok vice chairman Frankie Myers said in a statement that his tribe demands and deserves an equitable and fair approach to sharing water.

"For too long ranchers have done what they please with no concern for those of us living downstream. It is time we manage the Klamath Basin together as a whole," he said.

"The State Water Board needs to act immediately to hold these illegal diverters accountable. We know the drought is tough on the agricultural community, but once these fish are gone, they are gone forever."