A conservation authority is a local, community-based natural resource management agency based in Ontario, Canada. Conservation authorities represent groupings of municipalities on a watershed basis and work in partnership with other agencies to carry out natural resource management activities within their respective watersheds, on behalf of their member municipalities and the Province of Ontario.

The 1946 Conservation Authorities Act provides the means by which municipalities within a common watershed can petition the Province of Ontario to form a conservation authority for that watershed to undertake programs of natural resource management. Conservation authorities are established as corporate bodies under the Act. There are currently 36 conservation authorities in Ontario.

Conservation authorities are mandated to develop programs to further the conservation, restoration, development and management of Ontario's natural resources. They carry out programs in natural hazard management on behalf of the province and municipalities, and may also carry out other programs that serve municipal interests, such as nature education, land conservation and management, recreation programs, and research. Management programs generally occur in lands known as conservation areas, restoration areas or wilderness areas, though not all lands managed are necessarily designated as such.

Conservation authorities' primary responsibilities are in natural hazard management and environmental protection. While all conservation authorities carry out natural hazard management programs, their roles in environmental protection vary significantly because these are determined by local municipalities.

Each conservation authority is governed by a board of directors made up of representatives from its member municipalities. The number of representatives each municipality can have is determined by the Conservation Authorities Act based on its population within the watershed. Board members act on behalf of the municipalities they represent. Boards collectively determine the direction of authorities including the programs they will carry out and operational decisions throughout the year. For most matters, each member is entitled to one vote, and decisions are made by majority vote. For voting on non-matching levies (levies against municipalities which are not matched by the Province), voting is done using a weighted vote, where each municipality has the same share of the vote as the share of the budget that it pays, except that no municipality can have more than 50% of the vote. If a municipality pays more than 50% of the budget, its share of the vote is capped at 50% and the shares of other municipalities are increased proportionately.

Conservation authorities are administered by a General Manager or Chief Administrative Officer who reports to the Board.

Conservation authorities' funding comes from a variety of sources. Conservation authorities have the power to generate revenue through fees and other self-generated revenue, and also the power to levy their member municipalities. As registered charities, they are eligible for certain government grants. Under Section 39 of the Conservation Authorities Act, the Province may also provide grants to conservation authorities.

Historically, conservation authorities' funding was split evenly between the Province and member municipalities. In the mid-1990s, under the Red Tape Reduction Act of the Progressive Conservative government, conservation authorities' provincial funding was drastically reduced from more than CA$50 million annually divided among all the authorities to $8 million, and the Province reduced the scope of its support to natural hazard management programs and programs for protecting provincially significant conservation land, although the $8 million in funding was exclusively for natural hazard management. Other programs were considered to be only in the local interest and the Province stated that those programs could be funded by municipalities if the municipalities wished them to continue. At the same time, the government provided conservation authorities with new powers to charge fees and generate revenue. As a result, most conservation authorities became more entrepreneurial to generate the revenue needed to continue their local programming. Funding was further cut by 5% to $7.6 million in 2000. In 2012, under the Liberal government, funding was cut again by 2% to $7.448 million, and in 2019, under the Progressive Conservative government, it was cut again by 48% to $3.58 million.