Water Guide

Marazion is subject to short-term pollution procedures. Each day in the season, the Environment Agency forecasts risk based on weather and other factors. If a high risk is predicted, warnings are issued and signage is put up advising against bathing. In 2024, there were seven such warnings. Typically water quality returns to normal after a day or so, but multiple warning days can occur during prolonged wet weather.

The catchment surrounding Marazion covers roughly 3,370 ha. The Red River flows through lowland and improved grassland; the south-facing slopes near Marazion contain Cornwall’s only Grade 1 agricultural land and are used for vegetable and horticultural production. Most remaining farmland is used for dairy and beef farming; around 20 farms operate in the catchment. The towns of Marazion, Goldsithney and Crowlas lie within the catchment and the Marazion Marsh Special Protection Area sits behind the beach.

Historically, bathing water quality at Mounts Bay was impacted by private discharges and combined sewer overflows (CSOs). South West Water’s sewage treatment scheme for Penzance and St Ives, completed in 1995, provided extensive sewerage and removed untreated discharges. Wastewater from St Ives is now pumped to Hayle sewage treatment works where it receives secondary treatment before discharge through a 2.7 km outfall. Further improvements to CSOs at Long Rock were made in 1998 and the Marazion pumping station CSO was sealed in 2001.

Seaweed (macro-algae) and phytoplankton are natural components of the marine environment. During 2021-2024, seaweed was present at Marazion on 51 % of visits and was sufficient to be objectionable on 48 % of visits. Despite this, the beach does not have a history of large amounts of seaweed. Phytoplankton blooms have not been recorded and the risk to human health from marine algae is considered low.

Beach-clean observations show no sewage debris, tarry residue or significant tar balls at Marazion. Litter was deemed objectionable on 4 % of visits and present on 66 % of visits.

South West Water’s Upstream Thinking initiative works with farmers to reduce animal waste entering rivers by fencing livestock away from watercourses, improving silage and manure storage, and raising awareness of pollution risks. Household misconnections are also an issue and are being addressed via CCTV surveys and remedial work.

• Check daily pollution warnings: via the Environment Agency’s bathing water quality page or local signage.
• Avoid swimming after heavy rain: bacteria levels may be higher due to runoff.
• Be aware of natural debris: seaweed and phytoplankton are part of the natural environment.
• Support catchment improvements: report pollution to South West Water.

The 2025 bathing-water profile for Marazion paints an encouraging picture: the beach enjoys good water quality, no storm overflows discharge onto it, and regular monitoring and pollution-risk forecasting help protect bathers. Historic sewage issues have been addressed through major upgrades to the sewerage network and continued investment by South West Water. Challenges remain—rainfall-driven runoff from farmland and urban areas can temporarily reduce water quality—but ongoing catchment management, farming initiatives and infrastructure improvements are helping to safeguard Mounts Bay’s bathing waters. Nearby beaches like Long Rock still require significant investment to reduce storm-overflow use; lessons learned there will further benefit Marazion and the wider South West Cornwall coastline.