North, offshore beyond the Mismaloya [1] cove, rise the green-brushed Los Arcos sea rocks, a federal underwater park and ecopreserve. The name comes from the arching grottoes that channel completely through the bases of some of the rocks.
Los Arcos is one of the best snorkeling grounds around Puerto Vallarta [2]. Get there by hiring a glass-bottomed boat in the lagoon or by taking on of the day cruises [3] from Puerto Vallarta.
Snorkeling near the wave-washed Los Arcos is a Puerto Vallarta “must do.” Swirling bunches of green algae and branching ruddy corals attract schools of grazing parrot, angel, butterfly, and goat fish.
Curious pencil-thin cornet fish may sniff you as they pass, while big croakers and sturgeon will slowly drift, scavenging along the coral- littered depths.
Links:
[1] http://www.moon.com/destinations/puerto-vallarta/puerto-vallarta/beaches/mismaloya-and-los-arcos
[2] http://www.moon.com/destinations/puerto-vallarta/puerto-vallarta
[3] http://www.moon.com/destinations/puerto-vallarta/puerto-vallarta/sports-and-recreation/day-cruises