The Qinling mountains in China are biodiversity rich. We studied one of the high-latitude lakes on Mount Taibai with a view to looking at how aquatic diversity responded to long-term changes in climate over the past 3500 years. We specifically looked at a group of single-celled algae called diatoms, as they are very sensitive to the environment. We found that these algae changed gradually over time, but they showed abrupt change during the period known as the Little Ice Age, about 400 years ago.