That photo was from a freak accident at a power plant. A number of goliaths were in the cooling canals of an oceanfront nuke plant. It is possible they could have been sucked in through the cooling pipes out in the ocean, but I am not sure there is any actual knowledge about that.
The canal is separated from the Indian River by a spillway that is controlled by the plant and used to release water from the canal not add it. The only other place the goliaths could have come from is the intake pipes. Is there a theory that they walked across the beach to get to the canal or how else would you say it is possible that they got into the canal?