Greese, H. 1991 June 25 I spent the day leading orientation walks for students in the OTS course w/ Bob Marquis. On each of three we saw 1 Eleutherodactylus vampfredi and one or more Anolis, and a total of 2 small groups of Ateles. June 26 Today we went w/ Rios Tropicales, a commercial river rafting outfit, on a beginners' level trip on the Rio Sarapiqui between La Virgen and Chelanate. As we put in at the bridge on the south end of La Virgen @ 1000h, a large (>2.5m total length) Spilotes pullatus appeared swimming (not frantically) from the west side and made more than half way across before sweeping downstream ~50 m to an area of rapids. The snake swam in wide lateral undulations, always head upstream and w/ @ the anterior 1-2 m easily visible - I suspect it was inflated. We were surprised it could maintain position in the rapids, which it did for a couple of minutes before achieving the boulder covered west bank and disappearing from our view. There were 7 in the raft: Ann Weeks (architect, U. Florida), Brian Tzaw (undergrad, Harvard), Wendy, Heidi, Charles, me, and our boatman. Other boatman traveled separately (usually ahead) in a kayak. We put out between Chilanate and La Guaria @ 1300h, having seen numerous up to 'Class