- Otters, Lutra lutra,have been seen in the Usk river at Sennybridge for decades. They have been heard calling in the upper parts of the Senni River. Farmers report seeing them rarely, if at all. However, their prints in sand at the bank and in the snow at the side of the river show that they visit the upper parts of the Senni River, even in winter.
- In 2010, a photo was taken of an otter, swimming close by and under water and another was seen at the same spot in 2013.
- A female otter and her cub were filmed in Senni at 22:47 on 29/06/2014. This infra-red video was taken on the bank of the River Senni, about a mile south of Heol Senni. The animals first banged against the tripod and camera trap, presumably investigating them in the dark, before moving downstream and turning to check the Spypoint HD-10 digital surveillance camera. Otter spraint was also seen on a stone in this spot.