The two-year-old pooch was out for her nightly walk with owners Julian Mole and Cathy Eaton when she got her leg trapped in an underwater suction pipe, dragging her under.
Julian and brother-in-law Bruce Grant dived into the freezing lake and stood chest-deep desperately holding Maddie's head above water for 40 minutes until the fire brigade arrived.
Julian, of Park Way, St Austell, said: "It was touch-and-go for a while because she was being sucked under. It was quite scary."
The 40-year-old paid tribute to the "amazing" emergency services, who battled for an hour-and-a-half to save Maddie.
At one point 11 emergency vehicles were on the scene near Carluddon, including fire crews from St Austell, St Dennis, Falmouth and Bodmin, and an off-duty vet who drove from Newquay to help.
"There were too many people to thank at the time and we were in shock to be honest," said Julian. "But now we'd like to say a big thank you to everyone for saving Maddie's life."
The drama unfolded at around 6.30pm on Monday as Julian and Cathy met Bruce and his four dogs for the walk they do every night.
Julian explained: "All of a sudden we heard yelping from the other side of the fence. We leapt over and saw Maddie struggling in the lake where she must have gone for a swim.
"Bruce and I jumped in and held her head above the water. Under the surface we could see her whole rear leg had been sucked into a hole in a pipe and she was being dragged under. Cathy called 999 and we were holding her up, trying to free her, for about 40 minutes until the first fire crew arrived and took over.
"Maddie was obviously in pain but somehow she kept quite calm. I think she knew she was in trouble."
At around 8.30pm, firefighters managed to cut the pipe and Maddie was hauled out of the water – with the pipe still attached to her leg.
"We couldn't pull it off as it would have cut right through her leg," said Julian. "Luckily a vet turned up and the worst injury she's got is a nasty gash that's cut through the tendons. We were all pretty shaken up but thank goodness she's okay and will make a full recovery."