The widespread presence of macroalgae (seaweeds) is persistent across years in the Hutt Estuary, but biomass is generally low and the algae is not entrained so growths generally do not result in degraded intertidal sediment conditions. Much of the intertidal habitat consists of smooth rock walls and regular flushing of the estuary removes macroalgae from intertidal areas, limiting rotting macroalgae and poorly oxygenated and sulphide rich sediments to very localised areas on intertidal flats. Areas near the Hutt River mouth are organically enriched with rotting macroalgae causing significant subtidal impacts. In the shallow sub-tidal waters near the Waione Bridge, sediments were very soft, organically enriched and highly anoxic and surface waters were black from the impacted sediments. The consistent widespread cover of opportunistic green macroalgae throughout the intertidal estuary strongly suggests elevated catchment nutrient inputs are promoting growth.

Stevens LM 2020. Hutt Estuary: 2019/2020 Intertidal
Sediment Monitoring Summary. Salt Ecology Report 056. Prepared for Greater Wellington Regional Council by Leigh Stevens, November 2020.