CWRM Project Causes Unintentional Fish Kill

The Commission on Water Resource Management (CWRM) initiated a project meant to improve conditions for native ‘o‘opu (gobies), but an element of the work instead killed hundreds of members of the fish population it was meant to help.

On Wednesday, a video documenting a substantial fish kill of gobies at the mouth of the Wailuku River was brought to the attention of the CWRM. Two days prior, CWRM began the installation of a fiberglass fish ladder on the face of the 22-foot vertical concrete wall located within the river’s flood control project just below the Market Street bridge.

With the assistance of the Wailuku Water Company and Mahi Pono LLC, streamflows were reduced to provide a safe work site for the contractors to install the fish ladder, according to a Hawai‘i Department of Land and Natural Resources press release. CWRM issued an order to temporarily suspend the interim instream flow standard (IIFS) for the whole week beginning Oct. 28 so that less water would flow downstream to facilitate installation.

The installation was completed late Tuesday afternoon and both companies were notified. On Thursday, CWRM officially notified both companies to reinstate the IIFS and return full regulated flow to the stream. Water was returned to the river by Mahi Pono on Wednesday morning and by the Wailuku Water Company earlier today at CWRM’s request, the release said.

Notwithstanding that low flows continued uninterrupted through the project site for the duration of the project, it appears they were insufficient to reach the stream mouth to sustain fish life, DLNR said.

Staff from the DLNR Division of Aquatic Resources (DAR) has discovered smaller die-off events resulting from low rainfall and declining streamflows during summer months, but the greatly reduced streamflows in connection with the fish ladder project exacerbated conditions resulting in this large fish kill.

“It is obviously ironic that our project to improve stream habitat for ʻoʻopu appears to have resulted in loss of hundreds of fish,” said CWRM Chair Suzanne Case. “We regret this situation and express our sincere apologies to the Wailuku River community for these events. The Commission thanks the community for its support of the fish ladder installation and will continue to work towards improving stream channel conditions in the Wailuku River.”

CWRM received funding from the US Fish and Wildlife Service in 2015 to improve biological connectivity in the river, following up on the findings of the Commission’s Nā Wai ‘Ehā contested case hearing that identified the 22-foot vertical structure in the flood channel as an obstacle to the upstream migration of the native ‘o‘opu.