Building a Better Bonfire on Your Lakeshore

Relaxing by a bonfire, as the hot summer day turns into a starlit evening, is a northern Minnesota tradition that spans generations. In days gone by, many of us burned leaves and brush from our lakeshore property right along the shoreline. But as development pressures have increased on our lake, lake experts are encouraging us to move our bonfire away from the shore in an effort to protect the lake.

The ashes from bonfires contain phosphorous, an abundance of which can stimulate an overgrowth of algae and aquatic plants. These plants decompose after they die, and in the course of several generations can cause a lake bottom to become mucky.

According to a recent University of Utah study, an average bonfire contains 22 pounds of firewood and produces enough phosphorous to raise the phosphorous level one part per billion in 350,000 gallons of lake water. With many lakeshore owners enjoying bonfires over the summer, that level of phosphorus can impact water quality.

Over time, the water quality consequences of bonfires may impact fish, aquatic organisms and drinking water. The amount of phosphorus that reaches the lake increases if a bonfire is located on sloped or sparsely vegetated ground.

Lakeowners can still enjoy wonderful lake-view bonfires by following a few simple guidelines.

1. Choose a location that is lake-friendly. Move your fire as far from the shoreline as possible, and try to site it above a well-vegetated, buffered shoreline to encourage optimal infiltration of sediments.

2. Dispose of ashes in a metal container, away from the shoreline. After the fire is properly extinguished, disposing of ashes far from the shoreline will minimize the opportunity for excess phosphorus to make it into the lake via wind or runoff.

3. Build a small fire pit with a dished-out bottom. This will encourage infiltration, rather than runoff, of any remaining ash during runoff events.

4. Keep the fire small, and avoid burning anything containing plastic, foam or paint. Small fires will produce less phosphorus. Plastics, foam and paint all contain harmful chemicals, which when burned can make it into the lake through runoff and rainfall.

5. Extinguish the fire completely. Never leave a fire unattended or leave it to smolder. Unintended wildfires temporarily denude a landscape in their aftermath - a situation that creates increased runoff and sedimentation in lakes.

For more information, contact Lakewaves@dnr.state.mn.us