Approximately 400 gallons of sewage entered Nuuanu Stream on Monday, out of 960 gallons discharged at 1330 Liliha St., the state Department of Health Clean Water Branch announced.

The sewage spilled from a clean-out cap; the possible cause was grease buildup in the sewer line, city spokesman Alexander Zannes said via email.

The city Department of Environmental Services recovered 400 gallons, while an additional 400 gallons entered a storm drain that emptied into the stream, which flows into Honolulu Harbor.

The remaining 160 gallons dissipated on the ground, Zannes said.

Warning signs were posted along the stream Tuesday at the College Walk, North Beretania Street, North Hotel Street, North King Street and North Nimitz Highway bridges.

The public is advised to stay out of the waters of Nuuanu Stream below North Kukui Street, and Honolulu Harbor near the mouth of Nuuanu Stream, until warning signs have been removed, the Clean Water Branch said.

“We usually like to see at least three days’ worth of water samples so we can see a trend in reduction before we cancel the advisory,” said branch Director Myron Honda.

As a big-picture trend, Zannes noted that Honolulu sanitary overflows have decreased from 200 sewage spills in 2006 to 26 at the end of the second quarter of 2018.

Wastewater advisories are also posted at 808ne.ws/2FPj9S9.