A cryptosporidium outbreak in the Wellington region was spread through a water playground in Kapiti.
Eleven cases of the illness have been confirmed and traced back to the Raumati Beach splash pad over the Wellington Anniversary weekend, in late January.
However, the splash pad was not closed for cleaning for another three weeks.
Regional Public Health officer Jill McKenzie said the facilities were not closed for cleaning until they were confirmed as the source of the outbreak.
Those who have had the bug should stay away from public swimming spots for at least two weeks, she said.