The Lake Simcoe Protection Act, 2008 ("Act") received Royal Assent in December 2008. The Lake Simcoe Protection Plan together with a General Regulation (O. Reg. 219/09) supporting the Act came into effect on June 2, 2009, and with them key provisions of the Act came into force.

The Act generally takes an ecosystem approach to the protection of Lake Simcoe, and is comprehensive in the issues addressed and multi-disciplinary in its approach to regulatory control. The Act addresses issues ranging from water quality degraded by toxins, pathogens and nutrients including phosphorus, to loss and fragmentation of natural areas, invasive species, adaptation to climate change, changes to the hydrologic cycle, and recreational activities. Targets include reduced phosphorus loads, achievement of the protection of 40% of the "high quality" natural vegetative cover within the watershed, naturalized riparian zones, maintenance of stream flow, prevention of invasive species introduction, and reduced beach closings for Lake Simcoe.

Policies in the Plan impact decision-making undertaken pursuant to the Planning Act, the Condominium Act and a variety of prescribed instruments including sewage works approvals and permits to take water under the Ontario Water Resources Act, Conservation Authority Act permits to develop, to interfere with a wetland or to change divert or interfere with an existing channel, work permits under the Public Lands Act, approval under the Lakes and Rivers Improvement Act, and licences pursuant to the Fish and Wildlife Conservation Act, 1997. Decisions pursuant to these statutes must conform to Plan policies. Proposals with "significant impact" on ecosystem health, including proposed settlement area boundary expansions, proposals near the Lake Simcoe shoreline or certain natural heritage features will also be affected by the Plan. There is some grandfathering for permits where development applications have already been granted. Municipalities are now required to bring their Official Plans into conformity with the Plan at the time of their five-year reviews.

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