Often the cells stay attached for a while. There are green chloroplasts running through the cell to perform photosynthesis. With this they can move slowly towards light or hide from bright light. Many species need water of specific quality. Some can only live in acidic water.
Marshes often have very spectacular shaped species.
To collect them it often helps to squeeze the water out of some water plants into a jar. Some filamentous relatives of the desmids are visible with the naked eye because they become so numerous they form large 'mats' on the surface of ponds, a common sight during summer. Most people don't realize what beauty is hidden inside the amorphous mass. In Spirogyra the chloroplasts lie in the cell like a spiral.