The U.S. Environmental Protection Agency released a report that found that there was no long-lasting or severe damage to fish and other aquatic life from the mine waste spill at the Gold King Mine in 2015.

An EPA-led contractor inadvertently trigged the spill that affected rivers in Colorado, New Mexico and Utah with run off from the abandoned mine that included wastewater laced with iron, aluminum and other metals, the Denver Post reported.

Part of the Animas River in Colorado closest to the spill was already so polluted by decades of waste spilling from inactive mines that the most vulnerable fish, insects and other aquatic life were already gone, the EPA said.

Further downstream, the spill appeared to have little impact on fish numbers, probably because the pollution was diluted and kept moving, so the exposure did not last long, the report said.

Another factor was that most of the metals in the plume remained in particulate form rather than dissolving in the water, the report said. Particulates are less harmful to aquatic life than dissolved metals.

The EPA’s conclusions appear to be sound, said Jason Willis, manager of Trout Unlimited’s Colorado Abandoned Mine Land Program. Willis helped gather some of the samples used in the report but was not involved in analyzing them or drawing any conclusions.

The report demonstrates the need to take action on wastewater draining from 250 inactive mines in Colorado and hundreds more in other states, Willis said.

Wastewater was already pouring out of the Gold King Mine at a rate of about 3 million gallons (11.4 million liters) a week, the same amount released in one day by the EPA-triggered spill, Willis said.

“The fact that it was seven days’ worth of Gold King helps put it in perspective,” he said.

The EPA analysis, first reported by the Durango Herald, used samples gathered from the Animas River in Colorado and New Mexico and the San Juan River in New Mexico. The Animas flows into the San Juan near Farmington, New Mexico, about 160 km (100 miles) downstream from the spill.

The samples were collected in the fall of 2015, after the spill, and again one year later. The EPA used its own data along with samples collected by other federal, state and tribal agencies.

The report said potential longer-term impacts are still unknown, especially on longer-lived fish. Possible effects on very young fish — which are more sensitive to pollution — might be hard to detect because dead larval fish are harder to see than dead adults.