Slow worms in the pond

On Tuesday I saw my first slow worm of the year whilst planting some annuals in the wildflower border. Around this time last year we had to fish two different adult slow worms out of one of the ponds. I've been searching through my natural history books and on the internet, but there's very little information on slow worms and water. They clearly can swim, but whether or not they entered the pond intentionally and whether they were capable of getting out on their own I've no idea.