Hundreds of Dead ‘O‘opu During Fish Ladder Construction at Wailuku River

October 31, 2019, 4:43 PM HST · Updated November 1, 1:58 AM
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A video documenting a substantial fish kill of native ‘o‘opu (gobies) at the mouth of the Wailuku River was brought to the attention of the Commission on Water Resource Management on Wednesday during the installation of a fish ladder that is meant to help such species survive by ensuring mauka to makai water flow.

Maui resident, Jacob Kaneakua took video of the fish kill at around 11 a.m. on Wednesday.  He said he got a call from some friends who were walking up the beach and river and came upon the dead and dying fish.  In an attempt to save the fish, Kaneakua and his friends loaded up coolers with the stranded fish and ended up taking a few hundred back upstream where they had a better chance of survival.

CWRM Chair Suzanne Case said, “It is obviously ironic that our project to improve stream habitat for ʻoʻopu appears to have resulted in loss of hundreds of fish.  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.”

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On Monday, 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.  CWRM issued an order to temporarily suspend the interim instream flow standard (IIFS) for the whole week beginning October 28, so that less water would flow downstream to facilitate installation.

The installation was completed late Tuesday afternoon and both companies were notified.  Today 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.

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.  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.

CWRM received funding from the U.S. 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.

According to NOAA, a fish ladder, also known as a fishway, provides a detour route for migrating fish past a particular obstruction on the river. The ladder contains a series of ascending pools that are reached by swimming against a stream of water. Fish leap through the cascade of rushing water, rest in a pool, and then repeat the process until they are out of the ladder.

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