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Macrobrachium americanum (found from Baja California to the Galapagos to northern Peru), the sister species of M. carcinus in eastern drainages of the Americas (from Florida to the Antilles to southeastern Brazil).
It's without a doubt Macrobrachium hancocki, related to M. crenulatum on the Atlantic versant. The metallic blue coloration is very characteristic.
It's a Macrobrachium tenellum (the Pacific sister species of M. acanthurus in Atlantic watersheds of the Americas).
No true crayfish are native to Costa Rica, so anything of similar body form seen in a stream or river there is almost certainly a member of this genus. (That said, the aquaculture industry has brought the North American Procambarus clarkii and the Australian Cherax quadricarinatus into worldwide circulation, so it's possible that some have ended up either deliberately or accidentally introduced.)
Native crayfish are in fact entirely absent from Mesoamerica south of Belize and Guatemala, and from all of tropical South America (a few species are found in the temperate southern portions of the continent).
