We have recently refurbished the resistivity fish counter at Manley Hall gauging weir on the River Dee for Natural Resources Wales (NRW). The works involved a complete replacement of all the electrode on the true left weir and the installation of a conductivity probe.
The counter works by measuring the change in resistance of the water as fish swim over the electrodes and records their length, as well as whether they were moving in an upstream or downstream direction. The conductivity of the river water can sometimes affect the accuracy of the fish measurements and the counter corrects for this by measuring the resistance of the water using the conductivity probe and applies a correction factor. Fishtek also installed the fish counter on the right bank in 2014 during remedial works for the weir. The now completed fish counter will provide important data, including the number and size of fish (namely migratory salmonids) moving upstream in the River Dee.