Water Safety Throw Bag (Eastcote HA5)

I take cyclists out on led rides and sometimes we pass on canal towpaths or by other bodies of water. It's never happened yet but I'd like to be prepared for the eventuality of someone accidentally falling into the water.

I've been made aware that it is best practice to carry a "throw bag" on these rides - something to throw to the person who has fallen in so they can be pulled out. Does anyone have such a thing that they are not using and could be put to use by a volunteer leading cycle rides?

Many thanks in advance!