Answer: sandbars

AnswerCrossword Clue
SANDBARSMariners obstacles
SANDBARSRiver hazards
SANDBARSCoastal shipping perils
SANDBARSShoals
SANDBARSNavigation hazards
sandbarsSANDBAR, a ridge of sand formed in a river or the sea
sandbarsA long, narrow sandbank, esp. at the mouth of a river