Loughs Agency is advising anglers to help preserve salmon and trout stocks in rivers following prolonged periods of hot weather across both the Foyle and Carlingford catchments.
These extreme weather conditions have led to low river flows, high water temperatures and low oxygen levels in many bodies of water.
The guidance comes after only 43% of the average rainfall fell in Northern Ireland last month, although some rivers in the Foyle catchment also experienced severe flooding. Each one of these significant weather events put stress on fish.
Head of Science, Dr Sarah McLean is hopeful that anglers will proceed with caution on the rivers, particularly when fishing in the current warm temperatures.
Dr McLean said: "Many of our fish species will find survival difficult in these warm conditions without the added pressure of angling stress. Even catch and release poses a risk in these conditions as low dissolved oxygen in the water can result in poor fish recovery rates and inadvertent mortalities.
"It is also worth remembering that high water temperatures and low dissolved oxygen levels may also leave fish more susceptible to parasites and disease, so any fish caught will also require additional care when handling."
There are several measures anglers can take to help protect fish during the hot weather:
Anglers should report distressed or dead fish in the Foyle or Carlingford catchments directly and promptly to Loughs Agency at +44 (0)28 71 342100 or firstname.lastname@example.org.