Splash and Play in Coventry's War Memorial Park has been closed after parents said three children suffered diarrhoea and high temperatures after playing in it on Monday 3 August.
Natalie Jordan said her son and two others were ill the following day.
Coventry City Council said it is awaiting the results of microbiological contamination tests.
Ms Jordan said there were eight children who went to the park and three went into water feature, including her son, Finlay.
The following day, she claims, Finlay felt unwell and by Wednesday had headaches and a high temperature.
She said he was later diagnosed with scarlet fever, a contagious bacterial infection.
"We just think it's a little bit of a coincidence that it was just the three children [that went into the water park] that are poorly," she said.
According to Ms Jordan, one of the three mothers who went to the park has complained to the council.
The play area has 36 water jets, surrounded by other water features.
Andrew Walster, assistant director of Streetscene and Greenspace at the council, said there were a number of possibilities that could have made the children ill but further tests were being conducted.
He said they carry out daily tests for chlorine and pH levels and monthly checks for microbiological contamination and the most recent tests, on 31 July, came back all clear.
"We've taken a further sample on Saturday morning and we're currently waiting for the results. As soon as we have got them back, and assuming they are all clear, we will re-open the water feature."
Tests are being carried out on a park's water play area after several children fell ill.