Like his father and his grandfather before him, Fernandez is a mayordomo — the manager of a centuries-old network of irrigation ditches called acequias that divert water from the river into nearby fields. Hundreds of families in the Taos Valley rely on it to nourish their gardens and fruit trees and to replenish the aquifer they depend on for drinking water.

But the future of the Rio Fernando and its acequias is murky.

Early in the coming year, President Trump’s Environmental Protection Agency plans to roll back clean water rules, abolishing limits on how much pollution can be dumped into small streams and wetlands.

Federal data suggest 81% of streams in the Southwest would lose protections. A large share of streams in California and other Western states will be hard hit.

Nowhere are the stakes as high as in New Mexico. Environmental regulators in the state estimate that the new rule could leave 96% of the state’s waterways and wetlands unprotected from pollution from coal mines, factory waste, pesticide runoff and other sources.

And New Mexico does not have its own regulations to fill the void, which makes its waterways particularly vulnerable.

State officials warn that major tributaries to the Rio Grande could lose long-held protections, increasing the likelihood that pollution would flow into the state’s most important river. They include segments of the Rio Puerco, the river’s largest tributary in central New Mexico, and the Santa Fe River, which provides 40% of the city of Santa Fe’s drinking water.

Portions of those rivers are considered ephemeral, meaning water flows only occasionally due to rainstorms and snowmelt. Ephemeral waterways (sometimes called washes or arroyos) are common in Western states and are likely to become more so as warming temperatures make a dry climate drier.

These waters were subject to Clean Water Act protections under Presidents George W. Bush and Obama. They would not be under the new rule.

“We’re not just talking about little drainages, though those little drainages are critically important,” said Rachel Conn, projects director for the Taos-based environmental group Amigos Bravos. “It’s also these larger iconic New Mexico rivers that are on the chopping block and potentially open for pollution.”

The proposal has left New Mexicans worried about how they will be able to defend their rivers and streams from upstream polluters.