Ponds or lakes containing a rich supply of organic matter, particularly nitrogenous compounds, often develop huge populations or “algal blooms” of blue-green algae which may make the water so green that objects only a few inches below the surface are entirely invisible.
These blooms are often seen in ponds and small lakes are sometimes formed by Anabaena, a filamentous form resembling a string of beads, or Coelosphaerium, a spherical mass of cells or by other blue-greens.