There are no streams, dangerous plants or animals in the Black Sea's waters.
The sea platform decreases smoothly from the coast (on a strip of 100-200 m) towards the open sea (the water is not very deep, 1-2m), thus eliminating all the risk factors.
Summer resorts, Constanta, Adamclisi Tropaeum Traiani, Histria Citadel, Danube Delta.
Mamaia, Eforie Nord, Costinesti, Neptun - Olimp, Venus, Mangalia.
Useful info on Romanian Black Sea Coast: