HONOLULU (HawaiiNewsNow) - From Waikiki to Laniakea, many of Oahu's most popular beaches appeared back to normal Wednesday after Tropical Storm Darby's torrential rains.
But health officials say looks can be deceiving.
The water may look a lot better, but a Brown Water Advisory remains in effect and will likely stay up until the weekend.
The state Health Department said storm water run-off can harbor dangerous bacteria, including leptospirosis.
And that's not all.
"We have unknown chemicals in there. Herbicides pesticides, animal fecal matter, plus you have flood debris," said Watson Okubo, state Department of Health Clean Water Branch.
At beaches on Wednesday, many residents and visitors were playing in the surf, not knowing about the dangers.
Manuela Cooper and her family are visiting from California, and was "shocked" after learning about the Brown Water Advisory.
"I'm speechless," she said. "In fact my daughter is taking a surf lesson right now."
Other visitors said they know about the advisory, but didn't know what it meant.
"We saw it on the news yesterday in the room," said visitor David Garner. "We didn't know it was actually here. We thought it was another island."
Health officials say just because the water isn't brown doesn't mean it's safe.
"We have cesspool issues where the water doesn't come out brown," Okubo said. "It looks pretty good sometimes. Even when manholes sewer overflows it doesn't come out brown. Usually it pretty much is gray."
The state doesn't post signs warning beachgoers of brown water advisories. But the information is posted online.
"We cannot be posting the entire coastline of the state of the state of Hawaii or the coastline of Oahu. We simply don't have the manpower," said Okubo.
Okubo says places like Keehi Lagoon, Kaneohe Bay and Waimea are of particular concern. Tests were done all over the island Wednesday morning. The results come in tomorrow.