When i was at school (a long time ago) i had a teacher that read us fantasy books, and there's one that has stuck in my mind that i'd like to track down and read again. It would have been around 1984-85, the story revolves around a girl who has to go on some quest that took her into a lake, the fish had a community down there and they could all talk (the pike was the bad guy). Before she could go, she had to swim to the middle of a lake (possible a different lake) to retrieve some magic water lillies that could be made into a mask that would allow her to breath underwater. That's about all i can remember. I've been trying to find out for years, does anyone recognise this and know what it's called?