A shark warning has been issued for the Swan River in Perth after a school of at least 10 were spotted just 100 metres from where a teenager was mauled to death two years ago.

It's the third day the sharks have been seen in that part of the Swan with beaches along the river closed.

At least 10 sharks were seen lingering beneath Fremantle Traffic Bridge.

"They're congregated there for food and like I said at this time of year when there's fresh water the fish push out towards the ocean and I think they're waiting there for a feed," fisherman Glenn Foxton said.

The school was reported to SharkSmart WA this afternoon.

"A school of bull sharks has been reported near the Fremantle Bridge multiple times over the past three days," it said.

"It is possible that the frequency and duration of

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