Before or during decomposition, algae may impart a green, brown or even reddish color to the water. Color can affect the Secchi disc reading. Table 3 lists color values associated with varying degrees of water color. Suspended particles dissipate light, which affects the depth at which plants can grow. Turbidity affects the aesthetic quality of water.
Lakes receiving runoff from silt or clay soils often possess high turbidities.
These values vary widely with the nature of the seasonal runoff. Suspended plants and animals also produce turbidity. Many small organisms have a greater effect than a few large ones. Turbidity caused by algae is the most common reason for low Secchi disc readings. Local volunteers take Secchi disc and other readings and the DNR provides computer data storage and annual reports.