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Lake Simcoe Region Conservation Authority

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​​Phosphorus Offsetting

Phosphorus Offsetting is about improving and protecting the quality of water in Lake Simcoe and its streams and rivers.

Phosphorus is one of the greatest threats to this watershed's health. While a certain amount of phosphorus is essential for a healthy lake, too much phosphorus fuels excessive plant and algae growth. When the plants and algae die, they consume oxygen from the water. This reduction in oxygen has a negative impact on our cold water fishery.

Our new Phosphorus Offsetting Policy, approved by the Board of Directors on September 22, 2017, requires that all new development must control 100% of the phosphorus from leaving their property. This is referred to as a Zero Export Target, which supports the Lake Simcoe Protection Plan's objectives.

As new urban growth occurs, phosphorus loads will be controlled to the maximum extent possible. Any remaining stormwater phosphorus that cannot be controlled would require an “offset" to achieve a zero net target.

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.