Cracks have started to appear in the ice on the Lake of Menteith
Curlers are being warned not to venture on to the Lake of Menteith as a rise in temperatures has begun to thaw the ice.
Local curling clubs had planned an unofficial curling tournament, or bonspiel, following a weekend of activity on the loch near Aberfoyle.
The official Grand Match was called off by the Royal Caledonian Curling Club on Friday over safety fears.
The Loch Lomond and the Trossachs National Park said conditions on the lake were now very poor.
The park's chief executive Fiona Logan said she had spoken to representatives from 12 local curling clubs on Monday who had assessed the condition of the ice on the lake.
She said: "The rising temperature and melted snow has created significant surface water making it impossible to play. Conditions are so poor now that professional players and local residents have stopped venturing on to the lake.
"Although the bonspiel would have been an amazing event to see, for people's safety we would strongly advise anyone thinking of visiting the lake not to make an unnecessary journey."
Weeks of freezing temperatures had frozen the lake
Scott MacDonald, a manager at the Lake Hotel in the Port of Menteith, said the temperature was currently 4C.
"There's probably an inch to two inches of water on the ice," he said.
"The ice is starting to get dangerous - I would not be walking on it."
The planned Grand Match - which would have been the first for 30 years - was cancelled over safety fears.
The Royal Caledonian Curling Club called the match off on Friday, saying the emergency services could not guarantee players' or spectators' safety.
Police were also concerned about high numbers of vehicles parking on local roads to get to the event.
Thousands of people visited the lake, frozen over for the first time since 2001, on Saturday and Sunday.
Local hotel owner Ian Fleming said it had been a "Scottish winter festival" on the ice.