"The proposed timeframe to meet the nutrient reduction target is too long," she said.
"We need clean water rules and stronger land use controls now, not just for Lake Rotorua but across New Zealand.
"Without stronger national rules to protect our lakes, rivers and streams we will continue to see our clean green image eroded, threatening our agricultural exports."
Ms Sage said voluntary agreements were not enough to clean up waterways.
"Dairy cows continue to access and pollute rivers and streams despite a decade of Fonterra's voluntary Clean Streams Accord. A 2011 MAF survey found almost half of Bay of Plenty dairy farms had waterways from which stock were not excluded."
Ms Sage said for water quality to improve the country needed national environmental standards to protect waterways from stock access, limit stock numbers in sensitive catchments and set measurable limits on nitrates and other contaminants.
"If councils then want to set stronger standards through their plans they can.
"Without strong national policies and standards, the threat of court action will see regional councils caving in to land users with long timeframes and weak plan provisions," she said.
However, Rotorua and Taupo Federated Farmers provincial president Neil Heather, said Ms Sage was completely missing the point.
"Humans have lived around the lake for nigh on a thousand years," Mr Heather said.
"While you can't turn that around at the click of your fingers, the hard work of farmers on advice from the likes of DairyNZ, councils and of course, the community, has paid off.
Mr Heather said the agreement was the next step forward for the lake and deserved to be held up as a national example.
"It is community team work and means the Greens have to decide if they are going to be part of the solution or part of the problem," he said.