How are some small bodies of water so crystal clear they look transparent? Isn’t debris and random pollution constantly falling into them from the surrounding environment? What keeps them so clean-looking?
In: Earth Science
I know some are fed by underground aquifers, such as [this one.](https://en.m.wikipedia.org/wiki/Kitch-iti-kipi)
Someone who knows about this will have to fill in the blanks because this is not my expertise at all. LOL
Lake Tahoe is famously clear.
From the website [KeepTahoeBlue.org](https://KeepTahoeBlue.org):
>One reason Lake Tahoe is so clear is that 40 percent of the precipitation falling onto the Lake’s watershed falls directly upon the Lake. The remaining precipitation drains through marshes and meadows, which are a good filtering system for water.
Generally you see clear lakes near mountains. The water running off the mountain is free from alot of pollutants, since there is little farming in the mountains. Often in mountainous streams, the bottom of the river is rocky, meaning that not much sediment (dirt, sand, etc) can be picked up to be transported to the lake. Less sediment equals more clear water.
It all depends on the local geography.
Up high in the mountains? Not many pollutants
Surrounded by vegetation? Filters everything out
In a low laying river valley? Murky AF
Two main issues: the first is that you are correct that there is not much debris falling into the waterbody, and definitely low fines content (low amounts of silt and clay, which are slow to sink) AND the water body frequently has no important current to re-suspend any such fines once they settle down to the bottom. “Pollutants” are generally not suspended solids, but are instead dissolved solids, and at the very low concentrations typical in a waterbody of reasonable purity, do not affect transparency of the water.
Any waterbody with an important input from a stream or river will have both currents and incoming suspended solids carried in the stream flow, and thus clarity will be reduced (unless the water body is huge compared to the stream influx rate).
If the region has little soil, and is mostly bedrock, then there will not be an important source of fine-grained suspended solids to muck the water up. This is why many high mountain streams and ponds seem so clear. Erosion is mostly still making larger-grained sediments that sink fast, and fines all keep on going downstream due to the elevated currents.
Bigger the body of water is, more likely it is to have drainage from the surroundings which bring sediment and nutrients. Along with currents caused by moving water or by wind to mix it all.
Also the kind of ground matters a lot. Nice sand and gravel ground doesn’t have much stuff to start mixing in to the water. While clay and dirt dominated landscapes do.
But if you look at why two bodies of water, which could be equally clear and clean looking, they might be so for totally different reasons.
What I haven’t read but is a reason as well are oxygen levels in the water. The elevation at which a body of water is (and, thus, surrounding air pressure) has an impact on the dissolved oxygen levels in the water. Plants and bacteria need a certain percentage of oxygen to flourish so lakes in mountains tend to be pretty clear because the oxygen levels are not ideal for growth.
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