The pieces of wood had 1.5in nails sticking out of them - making them a potential hazard.
Glasgow Humane Society lifeboat officer George Parsonage leapt into action when he was told wood was floating down the river.
He said the sharp ends could have damaged the 100 racing boats which are usually out on the Clyde at Easter, causing a risk to life.
Mr Parsonage said: "Putting the rafts in the water was a thoughtless thing to do.
"It may be a lovely idea but not on the Clyde."
The river hero believes the mini-rafts were made by a local playgroup and put in the water to see which travelled the furthest.
But the planks for the rafts were held together by nails which projected through the wood by around an inch.
Mr Parsonage warned racing clubs which use the river of the potential danger and set out to pull the planks from the water.
He said: "The nails would have punctured the body of a boat causing it to fill up with water with the sailor ending up in the river."
A single skull boat can cost around £6000 and work to repair the hull could cost several thousand pounds, as the vessel would have to be returned to the boat builder for the work to be done.
Mr Parsonage was also worried children might return to the river to see where their raft had ended up with the potential of getting into difficulty.
He suggested there was also the risk of youngsters making larger rafts they could sit on and taking to the water with potentially deadly consequences.