Press Release – Canterbury District Health Board Canterbury DHBs Community and Public Health unit has issued a health warning for the Hakatere/Ashburton River at Boundary Road and at the hapua (river mouth). The warning follows the finding of exposed and detaching mats of potentially toxic … Canterbury DHB’s Community and Public Health unit has issued a health warning for the Hakatere/Ashburton River at Boundary Road and at the hapua (river mouth). The warning follows the finding of exposed and detaching mats of potentially toxic algae (benthic cyanobacteria) at these locations along the river. Warnings also remain in place for the Hakatere/Ashburton River at Hills Road and SH1.