Water has high surface tension , or resistance to penetration or stretching of the surface. This is because of the cohesion of the water molecules due to hydrogen bonds. Water surfaces can support small objects that are denser that water and would otherwise sink. These include some aquatic animals. The viscosity of water is also affected by hydrogen bonds.
Viscosity is the resistance of a liquid to motion.
The viscosity of water is important to marine organisms. Water is not very compressible , even at the very high pressures of the deep sea, about 500 times the pressure at the sea surface. This property is also important to marine organisms. Water density decreases with temperature and increases with salt content. Freshwater is less dense than seawater.