Singapore's seawater is generally considered clean and safe for recreational activities like swimming and sailing, but it is heavily monitored due to the city-state's role as one of the world's busiest shipping ports. The National Environment Agency (NEA) regularly tests water quality at popular beaches like Sentosa, East Coast Park, and Pasir Ris, typically grading them as "Good" or "Very Good." However, because Singapore is a low-lying island with a massive urban drainage system, heavy rainfall can occasionally wash urban pollutants or sediment into the sea, leading to temporary discolouration or "no-swim" advisories for specific areas. Additionally, Singapore has made historic investments in "closing the water loop," using advanced desalination and NEWater recycling to ensure that even the water drawn from the sea is treated with extreme precision. While you might see large tankers on the horizon, the coastal waters are remarkably well-maintained for an industrial hub, though they may lack the crystal-clear "turquoise" aesthetic found on more remote tropical islands.