The city council has closed off the play area and advised members of the public to stay away from the park as a whole.
Many of the paths have been flooded and the river has become dangerous.
"It makes you wonder how people can say climate change doesn't exist when you see this," he said as the torrent of water rushed past.
Millhouses Park has flooded many times in the past most tragically in June 2007 when teenager Ryan Parry lost his life in the waters.
Ryan and his friends walked home from King Ecgbert School in Dore when buses were cancelled and stopped off at Millhouses Park en-route, where he fell into the deep, fast-flowing water in the swollen River Sheaf.
A major search and rescue operation was mounted but 14-year-old Ryan’s body was later recovered by police divers around a quarter of a mile from where he disappeared.
Although heavy rain is forecast in Sheffield for Sunday and Monday, water levels are expected to be lower than during the devastating flooding in 2007 and 2019.
Sheffield City Council’s Director of Street Scene & Regulations, Richard Eyre said heavy rain on Sunday afternoon would pass quickly to scattered wintery rain on higher ground.