President Joyce Banda told mediators on Sunday that this wont be done until the wrangle over sovereignty is settled.
Malawi, which sits to the west of Africa's third-largest lake, claims the entire northern half of the lake while Tanzania, to the east, says it owns half of the northern area. The southern half is shared between Malawi and Mozambique.
"My government is not at this time willing to entertain any interim agreement on say, the environmental issues or Tanzania usage of the lake until the sovereignty issue is resolved," Banda told a news conference after meeting two former African presidents, Joachim Chissano of Mozambique and Thabo Mbeki of South Africa.
They represent the 38-member African Forum for former Heads of States that is mediating in the 50-year-old lake dispute.
Banda said she would take the matter to the International Court of Justice if the group failed to resolve the issue by the end of September.
"Malawi's position is that we own the entire lake, except for a portion ceded to Mozambique in 1954 for mutually beneficial reasons. The law clearly supports that position," she said.
Chissano said his team would take Malawi's concerns to Tanzania and pledged to seek a solution within three months.
Malawi had pulled out of talks on the issue in October, accusing its northern neighbour of intimidating its fishermen, a charge Tanzania denied.
It returned to the negotiating table this year as the soured relations delayed exploration for oil and gas.
In 2011, impoverished Malawi awarded exploration licenses to British-based Surestream Petroleum to search for oil in Lake Malawi, which is known as Lake Nyasa in Tanzania.