Some bathing waters are more likely to experience water quality problems when it rains. When heavy rainfall is forecast, many local authorities will put up a notice giving a ‘Prior warning’ of pollution events at these bathing waters. ‘Prior warning’ notices do not necessarily mean that pollution will occur. These are used in a precautionary approach to protect bathers’ health by advising the public of possible short-term pollution events which usually last for only a few days at most.