The state Department of Land and Natural Resources says it has accidentally killed hundreds of native oopu fish it was trying to help during work to improve the stream habitat at Wailuku River.

The fish kill occurred when the water flow was interrupted while DLNR’s Commission on Water Resource Management was installing a fiberglass ladder — a structure which allows migrating fish passage around an obstacle — on the face of a 22-foot vertical concrete wall just below the Market Street bridge.

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

On Thursday, a video documenting hundreds of dead oopu, also known as gobies, at the mouth of the Wailuku River was brought to the attention of the commission, which is responsible for administering the state water code.

With the assistance of the Wailuku Water Company and Mahi Pono LLC, the commission issued an order to reduce stream flows to provide a safe work site for the contractors to install the fish ladder. The commission issued an order to temporarily suspend the interim in-stream flow standard for the week, starting Monday.

The fish ladder’s installation was completed late Tuesday afternoon, and the commission notified both companies to restore the full, regulated flow to the stream. Mahi Pono returned water to the river on Wednesday morning, and Wailuku Water Company did so on Thursday.

However, during the duration of the project, not enough water was able to reach the stream mouth to sustain fish life.

Staff from the DLNR Division of Aquatic Resources discovered smaller die-off events resulting from low rainfall and declining stream flows during summer months. DLNR admitted, however, that the greatly reduced stream flows from the fish ladder project exacerbated conditions and resulted in this large fish kill.

The commission in 2015 received funding from the U.S. Fish and Wildlife Service to improve biological connectivity in the river. The 22-foot vertical structure in the flood channel was earlier identified during the Na Wai Eha contested case hearing as an obstacle to the upstream migration of native oopu, DLNR said.

The video was posted to Facebook by a local resident, who asked others to help save the fish by transporting them to higher waters upstream. The post elicited many critical comments from the community.