Hundreds of rotting dead fish and crabs washing up on a beach in Western Australia's Mid West are sending tourists away in droves and causing local businesses to suffer.

Residents of Jurien Bay, two hours north of Perth, are fed up and are looking to the State Government for answers.

For the past 14 years, rotting seaweed has infested the town's harbour, being pushed in by winter storms and depriving the water of oxygen, resulting in large scale fish kills.

One of the biggest kills was in November 2013, when thousands of fish were found floating dead in the water or decomposing on the shore.

Despite years of remediation works, the beach had to be closed last week after another influx of dead marine life.

Ian Stiles from the Jurien Bay Marina Action Group says the smell is unbearable and is deterring tourists from visiting the town's popular reef marine park.

"It smells like rotten eggs," he said.

"It's virtually like having a sewerage dump right next to Uluru or the Sydney Opera House; you're passing by a horrible smelling place to visit a scenic attraction."

The Department of Health is warning people not to swim in the water or eat fish caught in the marina.

It says the unpleasant hydrogen sulphide gas given off by the rotting seaweed can cause headaches, nausea and mild anxiety.

School children no longer have a safe place to learn to swim while cray fisherman are losing income because their catch is being poisoned by the polluted water.

Former Jurien Bay skipper Craig White says he and his family moved town because the problem was having too large of an impact on his charter business.

"If I was directly responsible for killing that many fish, I'd be locked up in jail, it's at simple as that," he said.

"In today's day and age it's unbelievable that this could happen.

"We had a major algae bloom on our boat, so did a lot of other boats and that was quite incredible, I'd never seen anything like that. It cost us a lot of money and time to get that removed.

"I don't know what it was doing to our health down there, we had reports of co-workers getting ill from on it.

"We had a live bait tank on our boat with live fish in it and we'd come back to the marina and the fish would jump out of the tank - they'd rather die on the deck than be in that water.

"We were getting boats stuck going out stirring up all the rotting weed and all of that - the smell was absolutely revolting and pretty embarrassing when taking customers in and out to the so-called pristine spot of Jurien Bay.

"If you actually did go in the water, if you were wearing any silver it would instantly go black. Anything like brass would go black and sort of a rainbow colour would leach out of it.

"We decided to get out of Jurien for the winter to try and avoid all that and move our operation up to Kalbarri and since we've been here we've actually fallen in love with the place and decided to stay here full time."

'We're not going to send customers there'

Kerry Rodan owns a local tackle shop and says her customer base has dropped significantly.

"When there is a fish kill or the marina deteriorates, we notice that there is a drop off with customers coming into the shop," she said.

"We're not going to send customers there in any case.

Dead crabs in Jurien Bay ( ABC: Gian De Poloni )

"Crabbing and fishing is a big past time for locals and also tourists that come to town and we supply these people with their bait.

"They're not going to come into the shop if they know the marina is dying or has this fish kill so it affects us in so many ways, not just us but also the town."

Ms Rodan says efforts to fix the problem are too little too late.

"I'm disappointed that when something is done it's a band-aid effect and it doesn't help alleviate the problem because it comes back again and it has come back yearly for a very, very long time," she said.

"We're only two hours away from Perth, we're accessible with a beautiful coastline and national parks and people are not going to come up here if they know the marina is not going to service their needs."

Hopes dredging program will bring relief

After the November 2013 fish kill, Moore MP Shane Love raised the issue in State Parliament.

After the 2013 fish kill, Moore MP Shane Love raised the issue in State Parliament. ( Supplied: Jurien Bay Community Resource Centre )

That promoted former transport minister Troy Buswell to commit to dredging the marina in the short term and also investigate a long-term remedy.

The Department of Transport says it is hoping information collected from wind and wave monitoring cameras at the marina will help it better understand the situation.

Sand excavation is also underway to deepen the channel to allow better water flow.

Mr Love says it is hoped a major dredging program due to start later this year will bring relief.

"Dredging is part of the answer and it is necessary," he said.

"It will provide for a healthier environment for some time to come but the problem will continue to occur if we don't get on top of the movement of sand and seagrass into the harbour itself.

"That's what the long-term studies are aimed at achieving."

Mr Stiles says he believes a lack of maintenance at the marina has allowed the channel to get narrower, trapping the polluted water within the bay.

"You've got an $150 million asset that hasn't been maintained. It's like building a bridge but not maintaining it," he said.

He is optimistic that the department is now on the right track to getting the problem fixed once and for all.

"I believe we'll finally find an engineering solution to it," he said.

"Busselton had a similar problem in the past five years and they seemed to have now fixed that."

The Department of Transport says it will continue to monitor water quality, while planning and environmental approvals are in progress for the dredging works.