KEKAHA — State officials are saying an algae bloom killed hundreds of fish in a drainage canal between Waimea and Kekaha during the first week of May.
But they aren’t ruling out an illegal discharge until investigations are complete into the report of a fish kill at the canal, known as First Ditch, starting about May 1.
That’s when dozens of people took to social media, circulating photos of piles of dead tilapia-like fish at MacArthur Park. And as the week wore on, more fish started washing ashore.
The canal does not currently flow to the nearshore area.
Kauai Department of Health officials responded to reports of the fish kill on Monday — after an unknown Good Samaritan spent the weekend cleaning up the carcasses.
Results from their testing point to low oxygen levels — 3.4 mg/l (milligram per liter) — that were most likely caused by a quick growth of algae.
“According to our staff, dissolved oxygen levels in the canal were lower than normal but not extraordinarily low,” said DOH spokeswoman Janice Okubo. “There were schools of tilapia swimming in the ditch as is normal.”
Okubo continued: “At this time, it is unknown as to what caused the fish kill, however, the presence of non-distressed fish within the canal suggests the cause of the kill may be more environmental in nature than due to an illegal discharge. However, an illegal discharge cannot be ruled out at this time.”
Algae blooms are a natural, often recurring event, that trigger low dissolved oxygen (DO) levels in bodies of water and can impact the rest of the ecosystem. DO levels can vary over time — even during a single day, depending on weather conditions and the number of fish or other animals that require oxygen in the water.
Periods of low DO are usually correlated with hot, sunny days when algae grows fast and “is especially bad at night, when algae consumes oxygen, instead of releasing it during the day,” according to DOH.
“It frequently occurs when there is little or no wind to agitate the surface of the water and large biomass; then, there is simply no oxygen in the water for fish to breathe,” Okubo said. “The only possible solution is to use aerators or other mechanical devices to oxygenate the water — or to get rid of the tilapia. This occurs occasionally even in large fish ponds.”
DOH is the primary responding entity to this fish kill. County of Kauai confirmed it’s not in their jurisdiction, Hawaii Department of Land and Natural Resources Division of Aquatic Resources currently doesn’t have an aquatic biologist on Kauai and National Oceanic and Atmospheric Administration’s Fisheries Hawaii spokespeople said they’d heard nothing about the fish kill.
DOH says their Clean Water Branch on Kauai is following up and connecting with local organizations and companies along the canal to ascertain who is responsible for the cleanup and whether there was an unreported discharge anywhere along the canal.
Jessica Else, environmental reporter, can be reached at 245-0452 or at firstname.lastname@example.org