Ontario will keep offshore wind turbines on hold despite being hit with a $25-million penalty under the North American Free Trade Agreement this fall for stalling a $5.2-billion Windstream electricity project in Lake Ontario near Kingston almost six years ago.

The environment ministry said two recently completed studies for the government on noise and environmental issues show more research is needed, but the province will monitor a pilot project Ohio is allowing in Lake Erie.

“The responsible choice is to keep the moratorium on offshore wind development in effect until all the potential impacts are fully understood,” the ministry headed by Glen Murray wrote a statement Thursday.

“Freshwater wind is in the very early stages of development around the world. While these latest reports provide real value in understanding some of its challenges, they are but one of the many steps necessary to allow for all of the proper research.”

Ohio’s project is “an excellent opportunity to better understand the impact of these developments on the Great Lakes,” the statement added.

Citing lost profits, U.S.-based Windstream filed a $568-million complaint under NAFTA after its 30-megawatt project was hit by the moratorium in February 2011.

At that time, the Liberal government of Dalton McGuinty was preparing for a fall election and facing opposition from anti-wind power activists, but denied it imposed the moratorium for political reasons.

But the province continued with land-based wind turbines.

Windstream has said it’s looking for an “amicable” solution to allowing its project to go ahead because its 20-year contract with Ontario to build the offshore wind farm remains in force.

Ontario and the federal government, whose lawyers handled the case, said they are “discussing next steps” about paying the $25 million award, the largest ever levied against Canada in a NAFTA challenge, plus $2.9 million in legal costs, to Windstream.

Officials would not elaborate on what the “next steps” involve or whether Ontario will be required to foot the entire cost.

The environment ministry said its decision to extend the moratorium is based on two studies totalling almost 400 pages.

One by Valcoustics Canada Ltd. warns that the impact of sound from offshore wind turbines is “different” from wind turbines on land, and travels longer distances.

As a result, offshore wind farms may have to be located further from land and inhabited areas than land-based wind turbines do. The study did not look at underwater sound issues, which could affect fish and other aquatic life.

A second study on decommissioning requirements for offshore wind projects in the Great Lakes — that is, when wind turbines are eventually taken out of service and removed — recommended such measures be included in the initial design stage.

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The study by GL Garrad Hassan Canada Inc. said, ideally, all turbines and related structures, such as offshore substations to collect power for transmission to shore, should be removed when a project comes to the end of its life.

There are about 10 gigawatts of salt-water offshore wind turbine projects, mainly off coastlines in northern Europe.