Councillors have called for the establishment of an independent environmental agency in the wake of the Lough Neagh toxic bacteria crisis.
Unionists on Armagh City, Banbridge and Craigavon Borough Council faced criticism for opposing the Sinn Fein motion calling for the setting up of a working group made up of representatives from central government and from the four councils bordering the lough.
Councilors voting against at the body's monthly meeting cited an Alliance amendment that called for the creation of the independent agency to act as a "regulator to ensure compliance with environmental law".
This amendment was accepted, with the majority of the council then voting in favour of the motion. All the DUP members, four of six Ulster Unionists, the TUV and Independent Unionist Paul Berry voted against.
Activists have previously argued for such an agency separate from the Department of Agriculture, Environment and Rural Affairs (DAERA). Currently, the Northern Ireland Environment Agency (NIEA) is under the control of the department.
Read more: Analysis: Much of the blame for Lough Neagh catastrophe can be laid at Stormont's door
The original motion called on the Northern Ireland Local Government Association (NILGA) to establish the working group. It passed despite unionist opposition.
It further urged the "development of a timebound targeted strategy to address the poor water quality and in particular the impact of toxic blue-green algae affecting Lough Neagh, and its impact on the environment, the lough's residents, businesses and recreational users".
The DUP wanted to add an amendment that also invited the Ulster Farmers' Union (UFU) on to any working group.
DUP Councillor Lavelle McIlwrath told the BBC his party broadly supported the motion but opposed the Alliance amendment.
Mr McIlwrath believed that if his amendment was included his party would have supported the motion but "it never got to that point".
Speaking to the BBC after the meeting, Alliance councillor Peter Lavery said it was "mind boggling that, against a backdrop of the ecological crisis in Lough Neagh, that the DUP and UUP opposed a motion for multi-agency action on blue-green algae".