​​​​​​Phosphorus Offsetting

Phosphorus Offsetting is about improving and protecting the quality of water in Lake Simcoe and its streams and rivers. ​While a certain amount of phosphorus is essential for a healthy lake, too much phosphorus fuels excessive plant and algae growth. Read more about phosphorus​.

Our new Phosphorus Offsetting Policy​, approved by the Board of Directors on May 26, 2023, requires that all new development must control post-development phosphorus loadings leaving their property to pre-development levels. This is referred to as a "post to pre" target, which supports the Lake Simcoe Protection Plan's objectives.

As new urban growth occurs, phosphorus loads will be controlled to meet pre-development phosphorus loading levels. Any remaining stormwater phosphorus that cannot be controlled would require an “offset" to achieve pre-development phosphorus loading levels.

The offset measure could include reductions in phosphorus elsewhere through the use of Low Impact Development techniques, or through retrofitting existing stormwater discharges elsewhere, preferably within the same subwatershed or in an adjacent watershed.