The trail is located just over the river. It's not always easy to follow. I got the information actually hiking it.
There is also a trail map.
https://www.nae.usace.army.mil/Portals/74/docs/Recreation/Otter%20Brook-Surry%20Mtn/2020SurryMountainLakeTrailMap.pdf?ver=2020-08-21-074957-607