Caterpillar

Caterpillar

Observation - Caterpillar - UK and Ireland. Description: Found in vegetation next to my garden pond. About 2-3cm long. I can't find this in Jim Porter's Caterpillars of the British Isles. Any ideas?

Found in vegetation next to my garden pond. About 2-3cm long. I can't find this in Jim Porter's "Caterpillars of the British Isles". Any ideas?