Lake

One can focus on almost any characteristic of water in a lake and see that the particular factor influences and is influenced by other characteristics of the same water. A profile of any given lake must take several of these factors into account. For example, salinity and temperature are two factors that seriously inhibit or promote life. High salinity does not favor most life other than some algal and shrimp growth. The Dead Sea, which has a salinity seven times that of seawater, has very low fertility. Temperature effects fertility both directly and indirectly. Most fish species prefer certain temperatures. While largemouth bass flourish at 75°F (24°C), trout prefer 50°F (10°C). Indirectly, temperature affects fertility by playing a large part in determining oxygen capacity of water. Warmer water holds less oxygen than colder water. Water at 45°F (7°C) can hold up to 12 ppm of oxygen; while 75°F (24°C) water can only hold a maximum of 8.5 ppm of oxygen.

Salinity remains relatively constant in some lakes, while it tends to increase significantly in others. A lake that has outflow, such as a runoff stream, keeps within a normal salinity range for that lake. But lakes that have no runoff lose water over time to evaporation, and a higher salinity results.

Wind plays an important role in water circulation, wave action, and surface temperature. On a warm, windy day, the surface water may be considerably warmer than the water beneath it. Since wind is directional and effects surface water more readily than lower water, it pushes warm water in the direction of the wind. The result can be a dramatic temperature difference between opposing shores of the same lake. The downwind shore may be as much as 30°F (16.7°C) warmer than the upwind shore. Strong winds can also create choppy waves that effectively decrease light penetrance.

Sunlight can only penetrate water to a limited depth. Both murky and choppy water decrease light penetrance. Submerged regions receiving light throughout are called euphotic. Since light is required by plants for photosynthesis, which produces oxygen, cloudy water generally has less oxygen. However, plants vary in how much light they require for growth. Some aquatic plants, such as hydrilla, can grow on the lake's littoral zone (part of the lake that slopes from the shore toward the benthos) 50 ft (15 m) under clear water. Other plants, like cattails, maidencane, wild rice, and lily pads grow in 3 ft (1 m) or less of water closer to shore.