Imagine algae that support aquatic life by converting carbon gas and sunlight into food and oxygen. They also serve as decorative sun-catchers and toothpaste enhancers, and can tell detectives what kind of water someone drowned in.

These tiny, glass-shelled powerhouses are called diatoms. They look like brown slime on submerged sticks and rocks. But under the microscope, they resemble starfish, flying saucers, or delicate strands of beads.

A teaspoon of Delaware River mud may hold tens of thousands of these single-celled plants, from 50 species.

Now, researchers from the Academy of Natural Sciences in Philadelphia and the University of Delaware are using them to unlock the river's past 150 years - and predict its future. Over the last three years, the academy's Donald Charles, Mihaela Enache, and David Velinsky, and Delaware's Christopher Sommerfield collected 40 cylindrical, four-foot-long cores of diatom-rich mud and silt from Delaware estuary marshes.

"Diatoms tell us about the biological response to changes in water chemistry and physical habitat," explained Charles, who is analyzing the diatoms in the cores.

Each species grows best under specific conditions, so diatoms in cores can tell us how salty or nutrient-rich the water was decades or centuries ago - even if the salt and nutrients are long gone.

The findings could be used to improve water quality and help officials respond to climate and sea-level changes.

So far, the researchers have found that nutrient pollution hit the northern Delaware estuary about 10 years earlier than the southern part, and that environmental regulations reduced pollution - although the benefits took more than a decade to help the diatoms.

The cores show how the Delaware has improved since the 1970s, said Velinsky.

"A lot of people consider the Delaware River a real mess," added Sommerfield, another lead investigator. "But it's actually a success story."

- Karen Knee