Mr McGowan also announced he will stop ships from entering West Australian ports unless they meet strict new rules that apply if they have come from "high risk" countries.
In recent weeks, a number of ships carrying COVID-positive sailors have travelled to WA, with 13 of the state's 15 active cases of COVID-19 stemming from either the MV Darya Krishna or the BBC California, both of which are berthed in Fremantle Port.
The new rules apply to ships that have stopped in jurisdictions, such as Indonesia, that have been deemed "higher risk" by WA Health authorities.
Under the measures, ships will not be allowed to change crews in those ports, sailors will not be allowed on-shore visits and maritime workers boarding vessels must wear appropriate personal protective equipment.
PCR testing of workers boarding the vessel will also be mandatory, as will rapid antigen testing of the crew onboard every two days, from when the ship arrives in the high-risk location to when the ship enters WA's waters.
Mr McGowan said evidence of negative tests could be made a condition of entry to the state.
"This is all about setting a new standard for the shipping industry so we can ensure we keep WA safe, especially given the highly-transmissible delta variant," he said.