Authorities say they are working to confirm reports a large shark has been caught and released by a member of the public in the Swan River, near the scene of a fatal attack that killed Perth teenager Stella Berry.

Ms Berry, 16, died after being bitten by what was believed to have been a bull shark on Saturday afternoon, in what was the first fatal shark attack in the river in 100 years.

Surf Life Saving WA reported a member of the public caught and released a 2.5-metre bull shark at 11:00pm on Wednesday at the East Fremantle boat ramp.

The boat ramp is less than a kilometre from where Ms Berry was attacked.

The catch was reported to authorities this morning.

In pictures posted to social media, a young fisherman claims to have caught the shark at the boat ramp about a kilometre north of where Ms Berry was attacked.

A shark alert has now been issued for swimmers in North Fremantle after the confirmed sighting of a bull shark — reported to be up to 3 metres in length — in the area.

A Department of Primary Industries and Regional Development spokesperson said it was "looking to follow up with the person who made the post today."

The Department also deployed a patrol vessel to the East Fremantle area, which will continue patrols throughout the day.

'Urgent' consideration of shark nets

Premier Mark McGowan said his government was "urgently" considering placing shark barriers in the Swan River in the wake of Ms Berry's death.

Mr McGowan said a full review into the "terribly unfortunate, tragic" attack was underway, and the government was also looking at whether barriers could be installed along the river "immediately".

"But whatever safety mechanisms, particularly those enclosures that give people peace of mind, we're looking at those as to where we might place one.

"Because what it does is provide families, particularly those with young children, some peace of mind, a bit like the one at Cottesloe or the one at Cockburn or some of the others up and down the coast.

"The risk of an attack is incredibly low, but I know a lot of people would appreciate that so we're just looking at what options are out there at the moment."

Shark fishing concerns

Shark Safety WA coordinator Leon Deschamps said shark fishing was dangerous behaviour in populated areas, as it increased the risk of a shark attack.

"Sharks aren't mindless killing machines by any means," he said.

"But when you're deliberately setting out to target a feeding shark, to bring in a shark that is hungry, then that's something which we don't want."

The ABC has sighted a picture uploaded to the social media app Snapchat on Saturday night in the hours after Ms Berry's death.

The picture, published by an unknown person, shows a line being cast in the Swan River near where Ms Berry was bitten, captioned: "Gone shark fishing."

Mr Deschamps said people who fish for sharks sometimes go to the lengths of dropping animal carcasses in waterways as an attraction, but that bait can last for days.

"Blind Freddie can see that dropping a whole pig carcass where kids swim is risking the lives of not just the kids, but anyone that swims," he said.

Shark fishing 'can't be controlled'

Mr McGowan would not say where the barriers could be installed, but said it was unlikely to include the location of Saturday's attack.

"I know there's some locations that a lot of people swim in, we'll have a look at those," he said.

"But there's all sorts of considerations about tidal movements and river movements and boating movements and that sort of thing that need to be taken account of, so it'll take a little while."

Mr McGowan said people fishing for sharks in the river was "not something I can control".

"It's just that there has been this tragedy, so we will review what can be done, what we can do better, what the circumstances are to make sure we make things as safe as we can."

Fremantle shark fishing ban

The legality of shark fishing in Western Australia is a matter for local councils, aside from a few select species which are banned under state law.