Volunteers from Foyle Search and Rescue have been battling the frozen Foyle in a bid to protect their pontoon.
The organisation, widely regarded at the city's fourth emergency service, worked through on Sunday night in freezing temperatures below -6 degrees in a bid to divert ice patches which had formed on the river from attacking the pontoon.
Foyle Search and Rescue said large floes of ice on the river are harming its pontoon and boats.
While they have been able to remain operational, the problems with ice and freezing conditions have been affecting their response times.
And they warned that further freezing conditions could put the Prehen pontoon out of action resulting in slower responses.
Adrian Boyd, one of the volunteers, said they worked for hours breaking ice patches up with shovels.
"It's been all hands on deck here," he said.
"Two tanks have busted and cracked and they will need to be replaced.
"Volunteers and members of the boat crews turned up here to try and cope with the ice.
"We've been out with shovels trying to break up the ice before it comes up to the pontoon. What happened is that ice formed further down the river and has travelled down here with the tide.
"We're trying to reposition the pontoon so we can avoid making a claim."
The charity's chairman, Craig Smith, said last year's bad weather cost them 90,000.
"Last January the ice froze right across the Foyle and it nearly sank our pontoon," he said.
"We had to get it lifted off.
"At the moment the ice isn't as high as that, but we're enquiring again about taking our pontoon off the water, which will cost us 13,000 alone."
Foyle Search and Rescue have already revealed that 2010 has been their busiest year ever.
Since 1993 dedicated teams from Foyle Search and Rescue have patrolled Derry's river bank in some of the most difficult circumstances.
The charity has also seen has seen donations decrease by almost 50%.