I am in Cardiff the capital city of Wales here in the UK .. we have a lovely lake in the city called Roath Park Lake. This morning we noticed a swan (with 3 sygnets) being circled by something in the water .. this 'something' would partially surface about every 30 seconds .. as it came closer the swan hissed and beat the water with it's beak .. the cygnets very sensibly climbed aboard. 2 things .. what could it have been in the water, and secondly why didn't the swan move away or seek dry land?

Looking forward to your reply,

Pat