Shamblers develop when Infected are exposed to large amounts of water, while more dry environments lead to the creation of Bloaters.

Where do shamblers come from?

It is suggested that Shamblers were in the process of mutating into Bloaters, but heavy exposure to water from the constant rain in Seattle caused them to change into Shamblers instead. However, they are encountered in areas away from water such as in the suburbs of the city and the forest areas.

Can shamblers see you?

Unlike the Clickers, Shamblers aren't blind and can spot you. This means you'll want to be extra cautious when skulking around an abandoned store or base. My personal method is to stealth kill every enemy I possibly can and then use Trap Mine to finish off the lone Shambler.