Karasu is a town an district of Sakarya Province in the Marmara region of Turkey. It has an overwinter population of around 24,500 which swells substantially in the summer to around 250,000 due to an influx tourists. Its municipal code is 264. Much of its commerce centers around hazelnut farming and tourism. It has a nearly 10 km coastline where many Turkish people train to work in foreign countries. People who live in the center of Sakarya often go to the Karasu seashore for the day in the summer.