A sea or body of water opposing another; opposing currents or tidal movements.
From counter- + sea (from Old English sæ). A nautical term combining prefix with the basic geographical feature.
Sailors historically used countersea to describe dangerous navigational situations where two sea currents or tidal systems opposed each other, creating chaotic water conditions. The Grand Raz (between Brittany and Jersey) is a famous example where countersea conditions create whirlpools.
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