The depth to which light can penetrate water depends on various factors, including the water's clarity, the wavelength of the light, and the presence of substances that can absorb or scatter light. Both freshwater and saltwater have similar characteristics in terms of light penetration, although slight differences may exist due to varying levels of dissolved substances.
In general, water absorbs and scatters light, causing its intensity to decrease with increasing depth. The absorption and scattering processes are influenced by the molecules and particles present in the water. These processes are more pronounced for shorter wavelengths, such as blue and violet light, compared to longer wavelengths like red and orange light.
On average, in clear oceanic water, sunlight can penetrate around 200 meters (656 feet) before it becomes too faint for photosynthesis to occur. In less clear coastal waters or areas with high concentrations of suspended particles, the penetration depth may be significantly less, ranging from a few meters to tens of meters.
Freshwater bodies, such as lakes and rivers, usually have lower levels of dissolved substances and suspended particles compared to the open ocean. Consequently, light can penetrate deeper in freshwater environments. In clear freshwater, light can potentially reach depths of several meters or more, but this can vary depending on the specific water conditions.
It's important to note that these estimates are approximate and can vary based on local conditions and water properties. Factors like algae blooms, sediment runoff, and water pollution can further impact light penetration by increasing turbidity and reducing clarity.