A river is merely the sum of its tributaries. In the case of the St. Croix, those tributaries add up to more than 2,000 miles of waterways.

A recently-launched website from the U.S. Geological Survey lets you click on any point of any river in the country and see all the  streams which flow into it.

On the St. Croix, you see the rivers which make up the approximately 7,800-square mile watershed in Minnesota and Wisconsin – from the Ann River near Pine City, MN to the Yellow River, in Danbury, Wisconsin.

According to the site, the population of the 19 counties with a St. Croix stream in it adds up to about 1.5 million people.

Flowing phosphorus

The map can also provide an interesting perspective about recent efforts to reduce algae-causing phosphorus in the St. Croix.

The river from Stillwater to Prescott is listed as “impaired” due to too much nutrient-rich runoff, which hurts water quality. To understand the scope of the work ahead, look at how many miles of streams make up the river at Stillwater: Eighty-nine streams totalling 1,964 miles.

To eliminate pollution flowing into the river, clean-up will be needed along many of those miles of streams – slowing erosion and reducing runoff from farm fields, streets, lawns and wastewater treatment plants.

(Slate via Finn Ryan)