Rathmullan is classified as achieving Good Water Quality in 2025 based on the assessment of bacteriological results for the period 2022 to 2025. Rathmullan has achieved a Good Water Quality rating for the four consecutive years 2022 to 2025. Annual water quality ratings are generally calculated using monitoring results over a four-year period and are assessed against stringent bacterial limits to protect bather health.

Rathmullan beach consists of a sandy beach in Lough Swilly, which is confined by Rathmullan pier to the South and runs up past Kinnegar to the Glebe outcrop to the North. Rathmullan beach supports a wide variety of plant and wildlife species including otters. The Rathmullan Wood Nature Reserve contains a wide variety of trees. Activities at Rathmullan beach include swimming, kayaking, boating, sailing, power boating, jet skiing (outside the designated area), diving and other land based activities on the beach. The designated bathing area is approx. 0.142km2 and the extent along the water is approximately is 1380m. There is a deep gradient off Rathmullan Beach with the water depth reaching 1m approx. 10m from the water line.