Police launched the fourth and longest phase of Operation Redwater on Monday, visiting four sites operated by Chevron, Fortescue Metals Group and BHP Billiton.

Drug-sniffing dogs were used to search 1200 workers and their luggage over four days.

Police found no illicit drugs or drug paraphernalia during the operation.

Acting Deputy Commissioner Murray Smalpage said that was a "pleasing" result.

"Operations such as this are about deterrence as much as they are about enforcement," he said.

"It sends a clear message from WA Police and the industry that checks will be made, and it is pleasing to see that no illicit drugs were located on any of the sites."

Chevron recently joined four of the biggest players in the WA resources industry, including Rio Tinto and the Roy Hill Consortium, all of whom have zero tolerance for drugs and use regular drug testing to ensure worker safety.

Smalpage said he hoped more companies would join Operation Redwater in the future.

The searches target workers at regional airports at remote sites.

A Chevron spokeswoman told Energy News that Operation Redwater supported the company's safety objectives where their workforce was "fit for duty".

"We are working closely with the WA Police to support their efforts to eradicate illicit drugs from the community," she said.

Operation Redwater was launched in December 2014 when WA Police conducted drug detection activity at FMG's sites, including Christmas Creek and Cloudbreak, in the Pilbara.

Phase two, which took place in January 2015, saw WA Police conduct their search at a Pilbara airstrip used by both BHP Billiton and Rio Tinto.

In conjunction with the airport searches, heavy haulage drivers were also targeted for drug screening in an operational component of Redwater, called Operation Phaeton.

Phase three took place in January at BHP Billiton and Roy Hill mine sites.

Operation Redwater came about after a series of triggers in WA, starting with an FMG worker being arrested in 2014 at FMG's Hamilton worker's camp for possession and distribution of crystal meth and claims of drug problems surrounding FMG workers.

According to Smalpage at the time 40% of driver's drug tested in the Pilbara tested positive for crystal meth, the highest level in the state.

"The problem was a bit broader than we anticipated, there's synthetic cannabinoids being advertised, and fake urine available, we've had anecdotal evidence and intelligence about people being apprehended with urine bags concealed under their arm in case they're called for a drug test," he said at the time.

"After an approach to WA police by industry, we decided we would launch Operation Redwater as a high-visibility, no-tolerance approach to highly dangerous activity on a mine site.

"When you think of the equipment they're using, it's just mindboggling that people would be so stupid, but it would appear they are."