TORONTO -- Ontario's Liberal government insists it is "totally committed" to cleaning up mercury in a river near a northern First Nation, but says it will not do anything that could make the situation worse for residents of Grassy Narrows.

The remote community near the Manitoba border has dealt with mercury poisoning since a paper mill in Dryden, Ont., dumped 9,000 kilograms of the substance into the Wabigoon and English River systems during the 1960s.

Mercury concentrations haven't decreased in 30 years. It is still present in dangerous levels in sediment and in fish, causing ongoing devastating health and economic impacts in the community.

Ontario Environment Minister Glen Murray said Wednesday that the government would make sure the cleanup of mercury in the Wabigoon River was done "to the satisfaction of the chief and the health of the people of Grassy Narrows."

Grassy Narrows Chief Simon Fobister then issued a statement on Thursday inviting Ontario Premier Kathleen Wynne "to put this historic commitment in writing" and sign it alongside him in a ceremony so the community "can know it is real."

Fobister says until Wednesday, Ontario had committed only to further studies and to consider options for dealing with the mercury that contaminates rivers and lakes and destroyed a fishery that was the basis of the local economy.

But Wynne told the Ontario legislature on Thursday that her government won't take any steps to clean up the mercury that could stir up more of the chemical trapped in the sediment on the bottom of the waterways.

Wynne repeated the government's long-held position that it would not "act in contradiction of science" as it deals with the contamination.

"We are committed to doing everything in our power to clean up Grassy Narrows, to take that mercury out of the ecosystem, to make sure that we do everything and that we are as diligent as we can be," Wynne said. "But, as I have said many, many times, we will not make the situation worse."

Ontario New Democrat environment critic Peter Tabuns said he too took Murray's comments Wednesday to mean the government was finally prepared to take action.

"The people of Grassy Narrows, desperate for help, heard the words of the minister. My colleagues and I heard the word of the minister," Tabuns said Thursday. "Now that the minister has finally committed, when will the premier sign an agreement with the chief of Grassy Narrows and when will she begin the cleanup of Grassy Narrows once and for all?"

Outside the legislature, Murray said the government committed $300,000 to Grassy Narrows to work with John Rudd, the lead author of a study on the local mercury poisoning, and another $300,000 for government scientists to start to implement Rudd's suggested work plan to deal with the problem.

"We anticipate there will be additional costs coming forward once the work plan is complete and the measures to remediate the conditions in the river have been decided upon," he said. "That is not the government's decision. It will be led by the First Nations and the elders and they'll make decisions with us about which measures should be taken and in what order. Nothing has changed."

Murray said he meets monthly with Ontario Indigenous Relations and Reconciliation Minister David Zimmer and Fobister to oversee the implementation of the plan, and expected they would meet again Friday.

Japanese researchers have found people who were not born when mercury was dumped into the English and Wabigoon River systems by the Dryden Chemical Company in the 1960s show symptoms of mercury poisoning.

The researchers reported in September that more than 90 per cent of the people in Grassy Narrows and the Wabaseemoong (White Dog) First Nation show signs of mercury poisoning.

"We have borne 54 years of poison and inaction. We need a firm timeline and a realistic budget to get this cleanup done as soon as humanly possible," Fobister said Thursday. "We will not rest until our fish are safe to eat again."