In reply to Oxymel of Squill ) who wrote this in
ws.net, I, Marvo, say :

My little waterlily pond has a leak and I've given up trying to fix
it.

If it's not too late and you don't want to go the blueberry route, drain the
pond, throw half a dozen beaten eggs into it, then fill it with very hot
water (fit a hose to the hot tap). It fixed my leak.

Leave it for a week or so, then refill.