When sea water is examined under a microscope, it reveals a hidden world teeming with microscopic life and particles. The most prominent features are plankton—tiny organisms that drift in the water. These can include phytoplankton, like diatoms and dinoflagellates, which are plant-like and often exhibit intricate, geometric shapes and structures. Zooplankton, such as tiny crustaceans, larvae, and protozoa, are also present, moving with rhythmic, jerky motions as they propel themselves with cilia or appendages.

In addition to plankton, the water may contain microscopic debris such as mineral particles, organic matter, and tiny air bubbles. Occasionally, bacteria and viruses may be observed as well, though they are often too small to see without higher magnification. Salt crystals can also be seen, appearing as tiny, cubic structures that may form as the water evaporates on the microscope slide.

This microscopic view of seawater offers a glimpse into the diverse and dynamic ecosystem that plays a crucial role in Earth's biological and chemical processes, highlighting the richness of life even in a single drop of ocean water.