Department of Health officials have advised people to stay out of the canal behind the Waipahu Recreation Center after wastewater was discharged into it.
The discharge was found Sunday. Officials say it is believed to have been caused by debris from nearby construction.
About 5,560 gallons flowed from the construction site, which went into a storm drain before entering the canal behind the center.
The discharge has been stopped and the area was cleaned, disinfected, and deodorized Sunday afternoon.
Signs have been posted from the Waipahu Recreation Center to the Ted Makalena Golf Course and samples will be collected.