A seal has been spotted in an inner western Sydney river, prompting a response from wildlife rescue teams who worry it may be in poor health.

However the National Parks and Wildlife Service (NPWS) said there were no obvious health concerns, and they were keeping track of the animal’s movements.

Pictures posted to social media showed the seal resting on a slab of concrete by the water’s edge at the Cooks River in Marrickville on Saturday.

“Not very often you see a seal in the Cooks River,” Tim Gillard, who took the photos, said.

The Cooks River runs through inner suburbs to the south-west of the CBD, and empties into Gamay/Botany Bay next to Sydney airport.

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Gillard called the Organisation for the Rescue and Research of Cetaceans in Australia (Orrca) who sent a rescue team to the scene.

Orrca spokesperson Craig Ryan said the organisation, which rescues seals and dugongs as well as cetaceans, had been monitoring the animal since it was seen on Sunday 22 February near the river mouth in Kyeemagh, and were continuing to assess the situation.

The seal had explored several small creeks that flow into the Cooks: the group received reports of it “behind the bay” in Muddy Creek, and most recently in Wolli Creek and Earlwood.

The seal was last reported to Orrca on Sunday morning and Ryan said the group is “ready to respond” to any more sightings.

“Normally seals stray closer to the coast, they’re not regularly viewed in these locations,” he said.

Ryan said the seal appeared to be in a “declining condition”.

“It might need to get some rest away from predators, and new places to find food.”

Dr Vanessa Pirotta at Macquarie University said marine mammals were a common sight in Botany Bay, so the potential for one to make its way up to Wolli Creek was “obviously there”.

But Sydney’s waterways can be an unhealthy place to visit.

The Cooks River estuary was marked as having “fair” water quality in the NSW environment department’s most recent 2022–23 summer sampling , after being judged “poor” in its 2010-11 report card. Its “algae abundance” grading has declined since 2010-11 from “poor” to “very poor”.

A NPWS spokesperson confirmed a New Zealand fur seal was first reported at Kyeemagh boat ramp and has remained in the general area since.

They said it was not unusual for seals to be found in coastal inlets and other waterways.

“Although the animal is lean, it is active and has no obvious sign of injuries or other health concerns,” they said. They will continue to monitor the situation with Orrca.

But Pirotta said photos of the animal suggested it was in poor condition, compared with other fur seals seen in Sydney.

“You only have to look at the individuals that hop on the Sydney Opera House steps of what a good condition-looking fur seal should be looking like,” she said.

“From time to time, unfortunately, we see individuals that do present with poor condition. As a result this animal will likely be assessed by authorities to work out if this animal needs to be euthanised or not.”

Pirotta said despite the condition of this individual seal, “fur seal populations continue to recover, which is good.”

She said the seal sighting is a reminder that “we are sharing our blue backyard with these creatures”.

In 2012 another adult fur seal was spotted in Cooks River.

There is a 40m exclusion zone around seals when they “haul out” on land, according to Orrca.

Pirotta warned anyone who saw the seal to be cautious: “They can not only have a nasty bite, but [a] bite can come with infection as well.”

Ryan urged members of the public to call Orrca on (02) 9415 3333 if they view marine mammals struggling, or in unusual areas.