Coastal water quality improves during the COVID-19 pandemic: Maui, Hawai'i.

Coastal ecosystems are increasingly threatened by degraded water quality linked to agriculture, wastewater and changes in land-use. This study collected coastal water quality measurements to assess spatiotemporal trends and drivers of variability on the island of Maui, Hawai'i. We also utilized Hawai'i's COVID-19 visitor quarantine, which dropped visitor numbers on Maui by >99 %, to evaluate the effects of population on coastal water quality. Nitrate and turbidity were highest on the north shore and during the winter. This trend is likely driven by a combination of fertilizers associated with agriculture and nearby wastewater injection wells, and large swells, respectively. All sites exceeded the State's water quality standard (WQS) for turbidity, and many sites exceed the WQS for nitrate. During the COVID-19 pandemic, coastal water quality improved across many sites, which is likely related to the visitor population reduction and stay-at-home orders that resulted in limited use of beaches and roads.