Fowlea unicolor — Tikiri Keelback
This species and related species have enjoyed a wide range of genus homes since it was first described in 1799 (!), including Hydrus, Coluber, Natrix, Tropidonotus, Nerodia, Xenochrophis, Amphiesma, and now, finally (?), Fowlea. The move to Fowlea only happened in 2019. This would formerly have been called F. piscator until a 2022 study that concluded that the ones in Sri Lanka are now F. unicolor
This frog- and fish-eating snake mostly stayed underwater while my guide Udaya Chanaka and I waited for it to make a photo-worthy appearance. I don't think remember seeing any fish in this rock pond, but there were plenty of frogs.