Heavy rain from a low-pressure system has filled southern Taiwan's three biggest reservoirs to the brim — good news for water supply, but downstream residents need to stay alert as operators release the excess.

• Nanhua, Wushantou and Zengwen reservoirs all hit full capacity within four days after steady rain from a low-pressure band and southwest winds.
• Nanhua topped out first and is overflowing naturally, with a desilting tunnel opened to release water and flush sediment at the same time.
• Zengwen, the country's largest, jumped from about three-quarters full to completely full after more than 400mm of rain fell on its catchment since the 19th.
• Zengwen began controlled releases through its permanent river outlet, and water authorities are warning people downstream to keep away from riverbanks.

Outlook: Releases will be adjusted as more rain arrives, and southern Taiwan heads into the dry season with its water supply secure for a fourth straight year.