The Hutt River is now safe to swim in, after last week's rain washed away toxic algae which forced its closure in late November.
Swimmers and dogs had been told to avoid the river south of Kaitoke, as the algae can cause sickness or death if swallowed.
It can kill livestock and dogs, and cause vomiting, diarrhoea and skin irritations in humans.
Greater Wellington Regional Council said today that all the algae had been flushed away by recent downpours.
The algae is common across New Zealand, with 103 rivers having been closed in the past six years because of it.
A no-swimming warning is still in place at Richard Prouse Park in Wainuiomata, where Hutt City Council is investigating high levels of e coli.