Lake Atitlán is one of the few places in the world where you can do altitude diving — the lake sits at 1,562 metres above sea level, which changes decompression calculations and gives certified divers an unusual experience in crystal-clear fresh water. The ATI Divers operation based in San Pedro is the main provider, offering courses from beginner certification through divemaster and running guided dives for certified divers.
Visibility in the lake can be exceptional, particularly in the dry season. Below 15 metres the water is noticeably cold. The underwater topography includes submerged walls, volcanic rock formations, and what may be ancient structures on the lake floor. Dive tables and computer algorithms must be adjusted for the altitude, and the operation will brief you on this before any dive.