The quality of close to 60% of the rivers in the Northern Sound region is "unsatisfactory".
Of the 125 local river bodies that were assessed by the Environmental Protection Agency over the past four years, 71, or 57%, were found to be of "moderate" or "poor" quality.
The EPA warns Ireland is in danger of losing its excellent coastal water quality, unless urgent action is taken to reduce nitrogen from farms entering water.
Nationwide, 2,355 river bodies were assessed, 43% of which were "unsatisfactory".
Locally in the Northern Sound region, Monaghan fares the worst
Almost three-quarters of its rivers are unsatisfactory, with 41 of the 56 rivers assessed deemed to be of "moderate" or "poor" quality.
Across Co Cavan, 43% of the river bodies assessed were found to be unsatisfactory, with 30 of the 69 rivers assessed falling within the "moderate" or "poor" categories.
The EPA report says urgent action is needed to reduce the concentrations of nitrogen that is entering water, mainly from agricultural activity.
A breakdown of the local findings can be found below.
The report categorises the biological quality of a river into five classes: high, good, moderate, poor, and bad.
Cavan
69 river bodies assessed: 8 high, 31 good, 16 moderate, 14 poor.
Monaghan
56 river bodies assessed: 5 high quality, 10 good, 15 moderate, 26 poor.
