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Evaporation, diversions increase botulism risk at Tule Lake

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Last month, biologists and irrigators drained Tule Lake’s largest unit of open water to mitigate avian botulism outbreaks on Tule Lake National Wildlife Refuge.

Now, record heat and irrigation diversions threaten to undo that work.

Tulelake Irrigation District, Ducks Unlimited and the U.S. Fish and Wildlife Service teamed up to move thousands of acre-feet of water from the refuge’s larger, muddier Sump 1A to its smaller Sump 1B. They intended to eliminate as much shallow water (the ideal breeding grounds for botulism in late summer) as possible and encourage the germination of wetland plants.

But for the past three weeks, farmers on federal leaselands in the southwest chunk of the refuge have been diverting water from Sump 1B to irrigate grain, alfalfa and row crops like potatoes. That, combined with intense, unseasonable heat that has accelerated evaporation, has made the sump lose more than 1,300 acre-feet of water since the beginning of July.

“It started dropping like a rock,” said TID Manager Brad Kirby.

Kirby said the heat was more to blame than the irrigators, who according to his calculations make up 20% of Sump 1B’s water loss at most.

“It’s not our desire to see 1B dry, but I can’t control evaporation,” Kirby said. “The effect of diverting the minimal diversions that we are taking out of there pales in comparison to the evapotransporative loss.”

Tulelake Refuge - 7/16

Water from Sump 1B enters the irrigation canal for the Southwest Sump. 

Kirby said heavy smoke from the Bootleg Fire has actually slowed the evaporation, causing the sump’s level to stabilize over the past four days. TID has also put a limitation on the amount of water that can come out of Sump 1B to 15-20 cubic feet per second, or about 40 acre-feet per day.

When Sump 1A began to drain, TID and refuge managers didn’t actually know how much water it held, only being able to estimate it through a formula developed in the 1980s. Because decades of keeping the sump submerged had caused the lake bed to silt in so severely, blurring the line between water and land, less water was available to pump into Sump 1B than Kirby expected.

“We took what we thought to be an overly conservative approach to identifying the amount of water that was in 1A,” he said.

Irrigators and biologists had initially expected that some water from Sump 1A wouldn’t fit into Sump 1B and would be leftover to use for irrigation. Kirby said the district gave leaseland farmers a rough idea of how much that would be (making no promises), but that there wasn’t even enough water to fill Sump 1B after the chips fell. On top of that, a long stretch of unseasonably hot days meant the old formula underestimated evaporation from the sump.

Still, Kirby felt the district needed to provide some water to the leaseland farmers in the Southwest Sump, a significant portion of which has been idled due to the lack of surface water coming from Upper Klamath Lake.

“We’re trying to do everything that we can to keep some water in 1B and keep it from dropping as fast as it was, and try to get it to hold, while also minimizing the impacts to the community,” Kirby said.

The legality of the diversions is as muddy as the bottom of Tule Lake.

The Kuchel Act, passed in 1964, allowed the leasing of refuge lands for farming as long as agricultural activity was consistent with the refuge goals of “proper waterfowl management.” Farming grain and leaving some behind as bird food generally aligns with that directive, but some argue that the planting of alfalfa and row crops doesn’t contribute to waterfowl habitat or food.

Tulelake Refuge - 7/16

An irrigated field of a row crop in the Southwest Sump of Tule Lake National Wildlife Refuge. 

Kirby was not able to say how much of the irrigated leaselands are alfalfa and row crops versus grain.

The western edge of Sump 1B, closest to the “English Channel” that connects it to Sump 1A, is in decent shape, but water levels decrease further to the east to the point where some areas are almost dry. A colony of grebes on the north edge of the sump had abandoned their floating nests after the water turned to mud.

On the southeastern shore of the sump, a pump adds a small amount of tail water into 1B, attempting to make up for the water that’s leaving it either directly into the atmosphere or through a pump on the southwestern edge of the sump to be used for irrigation.

Rachel Zwillinger, water policy advisor for Defenders of Wildlife, said while she understands the drought has been hard on everyone in the Klamath Basin and farmers need to make a living, few areas are in as dire straits as Lower Klamath and Tule Lake National Wildlife Refuges, which haven’t received a full water allocation in decades and rely on the Klamath Project for water.

Due to this summer’s incredibly hot and dry conditions, a botulism outbreak on Sump 1B was probably in the cards even without irrigation diversions. But Zwillinger said that Project irrigators taking from what little water Tule Lake refuge does have certainly isn’t helping.

“Because wetland availability is already so limited, further diminishing it in any way is a huge problem,” she said. “It’s another big impact that further reduces habitat availability and increases the risk of disease.”

Kirby said the district is trying to increase the amount of water being pumped into Sump 1B to offset the diversions and some of the evaporation. Some private well owners have also opted to direct some of their water to the refuge to stabilize the sump level. He said TID is keeping refuge staff in close contact to update them on the situation.

“TID’s doing everything we possibly can to minimize that but also to save the vastly reduced crop acreage out there,” Kirby said.

Tulelake Refuge - 7/16

Water sits in the irrigation canal in the Southwest Sump of Tule Lake National Wildlife Refuge on July 16, 2021.

Tulelake Refuge - 7/16

Water sits in the irrigation canal in the Southwest Sump next to an irrigated field.