Then maybe it's a protozoan, a one-celled animal-like critter.

     

• Blob-shaped, with shape changing radically as it moves:  Amoebas are usually blob-shaped and move slowly, oozing into different shapes   video  
• Not blob-shaped, more symmetrical and rounded, with only parts of the shape changing
  • with one or two "propellars":  Flagellates have one or two whip-like flagella which may cause them to move fast:  movie:    
  • with many tiny "propellars":  Ciliates have many short whip-like hairy cilia which move them or sometimes sweep food towards them.   Cilia are sometimes too small to see unless your microscope is on its highest power and then the critter is moving so fast you have a hard time "catching" it.  Some examples of ciliates are listed below:
    • . 

    • One type of ciliate is the paramecium and similar egg-shaped or rounded swimming things
      Videos:  1   2   3    4   6

    •  

    • Another type of ciliate is called Vorticella.  It is shaped like a fringed funnel with a spring at its base. video
      Stentor is similar. A relative looks like a microscopic tree with a bell at the end of each branch..  MORE CILIATEs   use your "back button" to return to this ID key

If you haven't found your protozoan, it's ok.  But you could check a book about protozoa or try our protozoa links to find out which kind it is. 

• Is it
  • PROKARYOTIC (without internal organelles visible) or
  • EUKARYOTIC
    • unicellular (one-celled) or
    • multicellular 
      • In a rounded colony  or
      • In a long filament
        • Bright leaf-colored green  or
        • red or purple or blue or colorless:  These are 
          dead fibers from decayed leaves or sometimes
          from people's sweaters.  They don't count as
          critters, but they might be important indications
          of environmental conditions; so you could
          make a note of them.

 

Cyanobacteria or blue-green "algae" are photosynthetic prokaryotes with a blue-green tint.  They form a slimy scum on the top of ponds which have been contaminated with too much fertilizer or sewage.   Zooplankton can't bite through the slime, and other phytoplankton can't compete with them when phosphates are high and nitrates are low in the water.

Diatoms (eukaryotic) are usually identified by their golden color and glassy shell.   Some water samples are filled with the empty glass shells of dead diatoms.  Diatoms do have photosynthesis and chlorophyll.  They're edible for some zooplankton. Is your specimen gold (diatoms) or green (maybe desmids)?
more diatom pictures
Desmids usually are very large (for one cell) and with unusual designs inside.  more desmid pictures Is your specimen like these? Yes.  Then you know. NO; if it's green but without the fancy designs, maybe it's another kind.  Try the green algae

Green algae are usually the most important good algae in relatively clean creeks and ponds.  Some are unicellular, but others are either colonies or filaments, like this picture--> Notice that even though some cells cells are small, they're obviously eukaryotic
	This filamentous green alga is Spirogyra, one of the best-known algae.  The spiral is a huge but strange chloroplast.  A local but nationally-known jazz group named themselves after this species of pond scum.   more spirogyra pictures use your "back button"  to return to this ID key
Here are a few algae which form a colony Volvox   Hydrodictyon (water-net)	If you didn't find your algae, it's ok, but you might try our algae links  I just want to start over