WHO lives in a hole like this, was the question on everyone's lips after rumours that a crocodile is snacking on wildlife from the Old River Lea.

Armed with nothing more than a notebook, pen and camera the Guardian staff took their lives in their hands on a boat trip up river to the site of the Olympic regeneration park on the Stratford border with Leyton to find clues.

National newspapers and London radio stations snapped up our exclusive story two weeks ago.

We reported that evidence, including large holes on the river bank, suggests a crocodile or alligator could be responsible for the mysterious disappearance of large birds including a Canada goose and five cygnets. Fishermen also say dogs have vanished from the tow paths.

But the hunt is on to find out exactly what is lurking in the depths.

We set off up river from Bow Locks with Mark Gallant, conservation officer with the Lea Rivers Trust, who witnessed the attack on the Canada goose, and his crew, rivers officers Tim Pegg and Mike Heron.

As we donned our life jackets, Mr Gallant said: "Put it this way, whatever it is must be big and fast. One minute the bird was there and then, whoosh, it was gone. Never to be seen again.

"We've seen large holes in the river bank and that's what we'll be looking for today."

The goose met its demise a short distance upstream from the site of the future Olympic stadium, an area which has no public access.

We saw for ourselves that large holes, up to one-metre wide and set in the mud, would be perfect spots for a crocodile to bask.

Overhanging branches and shadowy shallows also provide perfect cover for a predator stalking its prey.

Anticipation was running high as we turned off the motor and drifted up the delta.

Mr Pegg steadily guided the boat under the trees and closer to the beast's lair, and Mr Heron bravely donned his waders to pull us further into the unknown.

Suddenly, a splash just a few feet from the boat raised everyone's expectations.

The sun flashed off the water and we quickly scanned its surface. Could this be the moment we had been waiting for?

A quick glance from Mr Gallant revealed that the river was home to at least one exotic creature, a red eared terrapin.

He said: "We have found terrapins along the rivers before and it's interesting that they have settled here. They were probably exotic pets that people decided they didn't want to keep. The question is, if they can manage to live here, is it possible for something like a crocodile or alligator to make it their home?"

According to Mr Gallant, the cleanliness of the river has improved over recent years. It is partially tidal and when the water levels are low it is possible to look right down on to the river-bed.

In spite of water quality improvements, fly tipping is a major problem and tyres, old shopping trolleys and bricks are littered in and alongside the river.

But, Mr Gallant explained, that it is unlikely the mysterious holes could have been dug by people wanting to burying the rubbish.

"There's industrial sites on both sides of the river, it would be difficult for people to get access to the riverbanks and for them to drag rubbish and shovels over the fences would be even more difficult.

"I'm sure if someone wanted to dig up a spot for burying rubbish they would be able to find an easier place," he said.

We investigated the holes and after closer inspection we were still no nearer to the truth.

Mr Gallant added: "Subsidence is a possibility, but I couldn't be 100 per cent sure about it."

Previously it had been suggested to the Guardian that Chinese Mittern crabs, another exotic species that we saw on our trip up river had caused the holes.

But the conservation officers pointed out holes made by these crabs and they generally span around 30 centimetres.

Mulling over all possibilities on our way back to safety, Mr Gallant said: "If it was a mittern crab that had caused the holes I would be very concerned, this would mean that we had a massively large crab living here. They don't grow large enough to be responsible for this. They too have been introduced to the river as non-native species."

Back on shore we were no closer to finding out what lurks beneath.

Mr Gallant said: "The truth is out there somewhere and we'll keep looking. I've seen so many unusual things in the river that it really would not surprise me if turned out to be crocodile or alligator. We need to keep our eyes on things to make sure other wildlife that lives here is OK."