What Causes the White Foam in the River at Falls Park?

You may notice that during the early spring, the Big Sioux River accumulates quite a bit of white foam all over Falls Park. What is this foam, and how does it accumulate? Is it safe?

Large amounts of phosphorus in the water causes this effect. When the river reaches the rocks at Falls Park or any other rocky area, the water foams up and gets caught in the pockets where it’s difficult for the tide to wash the foam away. So it accumulates until the temperature changes (or the Fire Department washes it away).

High levels of phosphorus is not typically found in bodies of water naturally. In this case here in Sioux Falls, it is likely caused by pollution in the form of industrial waste discharge, and runoff from pasture and croplands.

Though the white foam and phosphorus doesn’t cause any harm to the human body directly, the high phosphorus levels can cause problems by promoting excessive algae growth. Bacteria that feasts on dead algae consumes large amounts of oxygen in the water, killing off fish.

Phosphorus is such a problem, our neighbor state, Minnesota, introduced a permit in 2005 to reduce phosphorus discharged into the Minnesota River Basin. South Dakota on the other hand, does not have any regulations in place to control phosphorus pollution.

With the problems the foam has caused at Falls Park with children drowning and getting lost in the foam in the past few years, and the pollution issues, one would think our leaders should probably put some regulations in place to prevent so much phosphorus from getting into our waters.