Turn back the way you came.

From Wikiventure

You swerve around and race back the way you came. After all, mingling with twolegs only causes trouble, as the elders always say. Although you know you're not going the right way, you want to get as much distance between you and the place as possible. Soon you find yourself at a river. Of course! You think. RiverClan territory!

Now you'll...

Cross the river here. There are enough small islands to keep you above water.

Go back and try to find the lake.