The charity which incurred more than £5,000 costs trying to save the whale in the Thames says its fund-raising may be scuppered by internet pranks.
Only one can was used in the rescue bid, the group said
The British Divers Marine Life Rescue organisation is auctioning the watering can used by its team to keep the whale hydrated, via the auction website eBay.
The price has topped £115,000 but the BDMLR accepts bids may not be genuine.
The site said it has safeguards to ensure only real buyers take part but the auction may need to be restarted.
A spokeswoman for the website said they may suggest the BDMLR only opens the sale to pre-approved bidders.
"It's a shame, particularly because this is for charity," she added.
'Symbol of hope'
The 19ft (5.5m) northern bottle-nosed whale died on Saturday as rescue teams tried to take her back out to sea.
She first surfaced on Friday morning, capturing the attention of thousands of people who flocked to the riverbanks.
A post-mortem examination showed the whale died from a combination of problems including dehydration, muscle damage and failing kidneys.
The can has now been signed by a number of BDMLR members who took part in the rescue.
The group said the auction gives bidders a "chance to own a symbol of hope, a piece of history and donate to a worthy cause all at the same time".
By Tuesday bidding had reached about £10,000 when a spate of activity took the price to above £99,000 in less than an hour. The increases continued until it passed the £115,000 mark early on Wednesday afternoon.
"We are aware there may have been people messing about," said BDMLR director Tony Woodley.
The East Sussex-based group had earlier criticised opportunists trying to sell items purporting to have been used in the rescue attempt.
A watering can with a starting price of £1,924 was placed on eBay but later removed by the website.
"There was only one watering can used in the rescue attempt and we have it in a safe," said Mr Woodley.