Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: Liz on 01/10/2010 20:30:03

Title: What causes water to look cloudy?
Post by: Liz on 01/10/2010 20:30:03

Liz asked the Naked Scientists:
   
While recently wading/swimming in Hood Canal, I noticed cloudy water down-current from me. I initially thought it was sunscreen, then quickly realized it was not. The water was swirling much as simple syrup does; it wasn't something else getting mixed in the water just reflected light in a different way, as if it were thicker, or perhaps denser. Upon closer examination we realized it was happening all around but was much more pronounced in my "shadow." A few details that might be relevant: this is saltwater, but less than a mile up current is a power plant that releases very cold fresh water. This was not specific to me; when my friend got in, he had the same effect.
What do you think?

Title: What causes water to look cloudy?
Post by: Bill.D.Katt. on 03/10/2010 05:59:00

Did the effect disappear after a little bit? The first thing that came into my mind was a lot of tiny air bubbles. I'm not sure which part of Hood Canal this is, but some parts are a little polluted, and that might be part of it. I'm assuming that this is Hood Canal in WA, then as someone who lives on that side of the Puget Sound I can honestly say I am just wildly guessing.

Title: What causes water to look cloudy?
Post by: chris on 03/10/2010 08:58:22

Did the water feel "layered" in terms of there being hot and cold regions?

Hot and cold waters have different densities and hence can remain separated, even in a moving body of water. And because the density is different, the speed at which light travels in each will be different, causing light rays passing from one to the other to change speed and bend, producing a strange swirling pattern. You can see this if you look through the side of a glass containing water and ice cubes. Denser, colder water melting from the ice-cubes falls towards the base of the glass, producing a swirling pattern as it goes.

This could be happening in your waterway, especially given what you've said about the power-plant. It's also common in waterways to get very warm surface layers of water as the water runs across hot beaches and mudflats with a colder undercurrent of ocean / river water.

Chris

Title: What causes water to look cloudy?
Post by: LizK on 05/10/2010 01:25:10

All the water was far too cold to notice much difference! After further discussion,(and input from a local scientist friend) we thought it had to do with stratification of salinity. The saltiest and therefore densest water being at the bottom, possibly made more dramatic by the influx of freshwater. Then, when the water hit something, like my body or a dock pillar, those layers got disturbed and that dense, highly salty (and cloudier) water from the bottom was pushed up and became more visible. Any thoughts?

Title: What causes water to look cloudy?
Post by: chris on 05/10/2010 16:02:13

That's a really good thought, Liz. I hadn't considered that; the fresh river water and salty sea water may indeed have stratified in the way you suggest.

Chris