DENVER — Tribal officials with the Navajo Nation declared an emergency as a massive plume of contaminated wastewater from an abandoned Colorado mine flowed down the San Juan River on Monday toward Lake Powell in Utah, which supplies much of the water to the Southwest.

Some drinking-water systems of the Navajo Nation, which spans parts of New Mexico, Arizona and Utah, have shut down their intake systems and stopped diverting water from the river.

Drinking water is being hauled to some communities.

Navajo President Russell Begaye said the tribe is frustrated with the U.S. Environmental Protection Agency, and he plans to take legal action. An EPA-supervised crew has been blamed for causing the spill while attempting to clean up the mine area.

Elsewhere, farms along the Animas and San Juan river valleys in northwestern New Mexico have no water to irrigate their crops after the spill.

The yellow plume of wastewater stretches 100 miles and was three times larger than initially estimated, federal officials say. The EPA initially estimated it at 1 million gallons.

The water is laced with heavy metals, including lead and arsenic. It spilled from the Gold King Mine in the historic town of Silverton, turning the Animas River in Colorado a mustard yellow last week. It reached the New Mexico municipalities of Aztec, Farmington and Kirtland over the weekend.

The EPA has been unable to determine whether humans or aquatic life face health risks from the pollution.