The pond is likely shallow and basically a glorified wetlands and looks to be highly eutrophic. Dense algae bloom crashes could cause periodic strong oxygen shortages which would be enhanced by shallow very warm conditions thus causing fish kills.
Nephelometric Turbidity Unit (NTU) is an old standard method.
Here is a link to some examples of water color and how they relate to NTU.
http://www.water.ncsu.edu/watershedss/info/turbid.htmlTurbidity.
Several methods are used to measure turbidity. All of them involve measuring the amount of some type of light that can pass through a standard width of water.
A Formazin Nephelometric Unit (FNU) is similar to a Nephelometric Turbidity Unit (NTU) in that both measure scattered light at 90 degrees from the incident light beam, but the FNU is measured with an infrared light source according to the ISO 7027 method whereas the NTU is measured with a white light according to EPA method 180.1.
Background. From Wikipedia.
http://en.wikipedia.org/wiki/TurbidityTurbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
The propensity of particles to scatter a light beam focused on them is now considered a more meaningful measure of turbidity in water. Turbidity measured this way uses an instrument called a nephelometer with the detector set up to the side of the light beam. More light reaches the detector if there are lots of small particles scattering the source beam than if there are few. The units of turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU). To some extent, how much light reflects for a given amount of particulates is dependent upon properties of the particles like their shape, color, and reflectivity. For this reason (and the reason that heavier particles settle quickly and do not contribute to a turbidity reading), a correlation between turbidity and total suspended solids (TSS) is somewhat unique for each location or situation.
Turbidity in lakes, reservoirs, channels, and the ocean can be measured using a Secchi disk. This black and white disk is lowered into the water until it can no longer be seen; the depth (Secchi depth) is then recorded as a measure of the transparency of the water (inversely related to turbidity).
The Secchi disk has the advantages of integrating turbidity over depth (where variable turbidity layers are present), being quick and easy to use, and inexpensive. It can provide a rough indication of the depth of the euphotic zone with a 3-fold division of the Secchi depth, however this cannot be used in shallow waters where the disk can still be seen on the bottom.
An additional device, which may help measuring turbidity in shallow waters is the turbidity tube.[6][7] The turbidity tube condenses water in a graded tube which allows determination of turbidity based on a contrast disk in its bottom, being analogous to the Secchi disk.
Turbidity in air, which causes solar attenuation, is used as a measure of pollution.
