Police dogs in the US state of Colorado are having to be trained to ignore the smell of marijuana now that the drug is legal. New K-9 recruits will be trained to sniff out only the illegal drugs while older dogs that still react to cannabis will soon be retired.

A report from local KUSA said that Rifle Police Department was having to retire an older sniffer dog as he was unable to be retrained. That department has just received two new dogs that won't be trained to sense marijuana.

The two new dogs came after a 12-year-old resident set up a GoFundMe page to pay for the department's newest recruits. In a post on the fundraising page, the two dogs are said to be chocolate labradors and "are very happy in their new home."

According to the report, departments around the state will be bringing in the newly trained pups.

Colorado voters passed an ammendment at the end of 2012 that paved the way for cannabis legalisation at the beginning of 2014. According to the Good to Know website, set up by the Colorada Department of Public Health and Environment, legal weed is only available to over 21s.

The recreational use of marijuana can also only occur on private property, it is still illegal to consume marijuana products in public spaces. Importantly, as numerous states still disagree with Colorado on the legality of cannabis, it is illegal to leave the state with any marijuana products.

As a taxed industry, marijuana has been good for the local government too, with sales surpassing $1bn in the first 10 months of 2016 and breaking the same $1bn line after only eight months in 2017.

Cannabis use has so far been legalised in Alaska, California, Oregon, Massachusetts, Maine, Nevada, Washington and the District of Columbia, along with Colorado, though some of those states are still in the process of phasing in legalised recreational use.