Once a bathing water has been designated, the water quality is tested by Natural Resources Wales (NRW) to support the bathing season, which runs from 15 May to 30 September.
Ar ôl i ddŵr ymdrochi gael ei ddynodi, mae Cyfoeth Naturiol Cymru (CNC) yn profi ansawdd y dŵr yn ystod y tymor ymdrochi, sy'n para rhwng 15 Mai a 30 Medi.