Bathing beaches are important marine resources for many coastal cities. To safeguard the health of beach users, beach management authorities in Hong Kong rely on the use of the concentration of the indicator bacteria Escherichia coli (E. coli). Currently, the beach water quality grading system (from “good” to “very poor”) is based on the geometric mean of the most recent five measurements of E.coli level sampled at roughly weekly intervals – beaches can be closed when E.coli levels exceed permissible limits. However, the use of such sparse data (data spanning over a month) is problematic, as daily (or even hourly) E.coli level varies dynamically as hydro-meteorological and pollution conditions change. There is a significant time lag between the issued grading based on past measurements and the actual water quality, leading to outdated beach advisories. Worldwide there is an increasing realization that real-time beach water quality forecast – a most challenging scientific problem - can enhance the effectiveness of beach monitoring and public health protection.