SALEM — New requirements would be imposed on Oregon water rights transfers under a bill that environmental advocates claim is overdue but irrigators fear will block many transactions.

Water rights transfers would be prohibited under Senate Bill 427 if they reduce stream flows along a longer stretch of a waterway, which proponents say is needed to protect fish habitat.

“Stream flow is a vital issue for native fish and other aquatic species,” said James Fraser, state policy director for the Trout Unlimited nonprofit. “It would just make sure that proposed changes and moving water rights around do not make conditions worse for fish.”

Currently, water rights transfers cannot cause injury to other water users or expand the amount of water used, among other requirements.

Under SB 427, transfers that involve changing the point of water diversion would also be prohibited if they result in the “diminishment” of stream flows.

For example, if a water diversion is transferred upstream of its original location, the stream flows along the stretch of river between those points would be diminished.

In other words, even though the same quantity of water is withdrawn, flows would be reduced along a longer portion of the entire river, which environmental advocates argue is detrimental to its ecological health.

While regulations for new water rights take “modern environmental values” into consideration, the transfer of existing water rights does not, said Caylin Barter, a representative of the Oregon Water Partnership, a coalition of environmental groups.

“We have a loophole by which old water rights are bypassing the standards for new uses,” Barter said during a recent legislative hearing.

Updating regulations for water rights transfers is part of a movement to make Oregon law reflect the “21st century water reality” of increased scarcity, she said. “We have momentum to update outdated transfer laws.”

If stream flows are decreased along a longer stretch of a river or creek due to a transfer, lower water levels can create “bottlenecks” for migrating steelhead and salmon, according to the bill’s supporters.

Proponents of SB 427 also say that decreased stream flows counteract the principle of “dilution is the solution to pollution,” as contaminants become more concentrated along the diminished portion of a waterway.

“We must ensure we don’t diminish stream flows in systems that are already stressed,” said Jeremy Austin, wild lands and water program director for the Central Oregon Landwatch nonprofit.

However, irrigators and other water users claim that SB 427 will effectively prohibit many transfers at a time that new water rights are no longer possible to obtain in most waterways and aquifers.

“This bill represents one of the biggest threats to Oregon water law and policy that I have encountered over the course of my career,” said Steve Shropshire, an attorney representing the Oregon Association of Nurseries.

The state has entered an era in which transfers are becoming the “primary management tool,” so lawmakers should be trying to make regulations more flexible rather than impose sweeping new restrictions, he said.

“It is far from a narrow fix as suggested by the bill proponents,” Shropshire said, adding that SB 427 would likely be “weaponized” by opponents during the already burdensome transfer application process. “This sets the stage for years of time-consuming litigation.”

It’s also frustrating that environmental advocates who crafted the bill did not seek any advice from irrigators and other water users who’d be affected by the legislation, said April Snell, executive director of the Oregon Water Resources Congress, which represents irrigation districts.

“We have not been invited to provide any feedback whatsoever,” she said.

Several other agricultural organizations urged the Senate Natural Resources Committee against passing SB 427, joined by representatives of city governments and water utilities who said it’d impair or prevent their ability to replace water intakes — even if only slight relocations upstream are involved.

For example, the Eugene Water and Electric Board is planning to break ground on a new water treatment facility next year, which would be precluded by the bill, said Karen Kelley, its chief operations officer.

“It would keep us from being able to build this plant,” she said.