Koloa Landing has a horseshoe shaped reef with plenty of underwater life and tropical fish. It's actually an old boat launch but is now mainly used as a scuba and snorkeling spot. It's usually very calm all year round, and decent coral can be seen on the reef. The best spot to see fish is near the sides of the bay, and away from the sandy middle. Don't let the murky water by the shore scare you, it gets much clearer further out.
At one time Koloa Landing was Kauai's most important port. During the whaling was king, dozens of ships andchored here to trade with natives for provisions. In fact all delivers either came via Koloa Landing or Waimea. During plantation days, Koloa Landing was the departure and arrival port for passenger and cargo vessels as well.
Today no trace of these times exist however it still serves as a great spot to lanch a dive. Turtles can be seen usually in the morning or evening.