Bubbling stones

The pebbles in the pools left by the falling water level in the upper reaches of the River Wear were bubbling in the bright spring sunshine this morning. Scraping some of the thin film of slime from the stones onto a microscope slide revealed the cause – millions of minute, photosynthetic diatoms, producing oxygen bubbles. In amongst them I found several amoeba, like the one shown in the second-from-top photograph, grazing on these underwater meadows.