The calmness of the water in the Dominican Republic depends entirely on which coast you are visiting and the time of year. For the calmest, most "lake-like" waters, you should head to the Caribbean (Southern) Coast, particularly areas like Bayahibe, La Romana, and Boca Chica. These beaches are protected from the open ocean and are ideal for families with small children or those who enjoy tranquil swimming. On the other hand, the Atlantic (Northern and Eastern) Coast, which includes popular spots like Punta Cana, Puerto Plata, and Samaná, tends to be much more turbulent. In Punta Cana, while many resorts are protected by offshore coral reefs that create a calm "lagoon" effect for swimming, the water beyond the reef can have significant waves and strong currents, making it popular for surfing and windsurfing. During the winter months (December to February), the Atlantic side can see even rougher conditions due to "cold fronts" from the north. In summary: if you want absolute stillness, choose the south; if you enjoy a bit of surf and a lively ocean breeze, the east and north coasts are the most popular choices.