The concentration of dissolved oxygen in Darby Creek was measured to range from 7.4 to 12.4 milligrams per liter. The carbon dioxide concentration ranged from 1.9 to 3.4 milligrams per liter and the nitrogen concentration range from 2.1 to 2.2 milligrams per liter. The concentration of organic nitrogen ranged between < 0.19 and 0.25 milligrams per liter and the concentration of organic carbon ranged from 2.1 t to 2.2 milligrams per liter. The concentration of ammonia in filtered water was less than or equal to 0.02 milligrams per liter in two measurements and the nitrate concentration was half that in two measurements. The orthophosphate concentration in filtered water ranged from < 0.031 to 0.071 milligrams per liter and the phosphorus concentration in unfiltered water ranged from 0.032 to 0.045 milligrams per liter.