Its flower looked a bit like a buttercup but the plant was quite tall and straggly, its leaves were long and narrow, and it was growing in shallow water on the edge of the reedbeds at RSPB Lodmoor. I took a few photos and filed them away to check my books when I got home from holiday.

Please do correct me if I’m wrong but I think this is Lesser spearwort (Ranunculus flammula), the name spearwort coming from the leaf shape, which is described as ‘undivided and spear-like’ on the Wildlife Trusts website. The plant is said to be hairless, the stems red-tinged, the leaves slightly toothed, none of which can be distinguished in my extremely inadequate photos. The flowers are noted as being half the size of Greater spearwort but that only helps if you can see the plants side by side. I’m quite glad I wasn’t able to get too close to the plant though, as that Wildlife Trusts website also says the sap, if touched, can cause blisters.