They get their starts at headwaters, which may be springs, snowmelt or even lakes. This water then travels all the way to their mouths, usually another water channel or the ocean. The temperature is usually cooler at the source than it is at the mouth of the river. The water is also clearer at the mouth, has higher oxygen levels, and freshwater fish such as trout can be found here. Towards the middle part of the stream/river, the size of it increases as doe’s species diversity numerous aquatic green plants and algae can be found. Toward the mouth of the river or stream, the water becomes murky from all the dirt that it has picked up upstream, decreasing the amount of light that reaches the bottom of the river. Since there is less light, there is less diversity of vegetation meaning that you would find fish like catfish who can survive on little oxygen.
Intertidal Zone The intertidal zone is the zone in the foreshore and the seabed that is exposed. In the intertidal zone the most of the organisms are small and most are relatively uncomplicated organisms. This is for a variety of reasons; firstly the supply of water which marine life requires surviving is intermittent. Secondly, the wave action around the shore can wash away or dislodge poorly suited or more adapted organisms. Thirdly, because of the intertidal zone's high exposure to the sun the temperature ranges can be very extreme. For example the temperature could be extremely hot or extremely cold like in frigid climates.