The outlet is temporarily made to river Kupa until the construction of sewerage treatment plant construction.
Works on sewer were executed in phases. Part of sewer in Mrzlo polje was constructed in period before 1990. Works were continued in 1997 at Karlovac section: Kupa –Mekušje and in Duga Resa: TKL-Cotton industry Duga Resa. In the scope of sewer two river crossings under Mrežnica and Korana were constructed and the retention pool by the Mrežnica crossing.
Sewer diameter varies from 600 mm to 1100 mm at the temporary Kupa outlet.
The large problem for works execution was the alignment clearance of mines in Mekušje. Part of sewer in Karlovac and retention pool have been built gravelly soil with high level of underground waters. During the works execution method of ‘igloo filters’ was applied for underground water lowering.