The mobile application "Lake researcher" is designed and intended for students and adults of all ages. Using the application, with the help of just a few clicks on the screen, you will get to know the flora and fauna of the lakes, explore the environment surrounding the lakes and find out how strongly the lake is affected by the eutrophication process.Most water bodies, including both lakes and our Baltic Sea, are currently suffering from eutrophication. Eutrophication is a phenomenon when, due to an excessive amount of nutrients in the water, algae and other vegetation are overgrown and the balance of organisms is disturbed.We humans are the biggest contributors to lake eutrophication, because the main nutrients that promote eutrophication are phosphorus and nitrogen, which are widely used in our daily activities and in the farm.Using this mobile application, you will not only study the state of the lake, but also learn to observe, analyze, evaluate the environment and the processes taking place in it.The mobile application was developed during the implementation of the project "Improving the management and maintenance of the lakes of Kurzeme and Northern Lithuania" (Project no. LLI449) (acronym: LIVE LAKE). The project is financed in 2014-2020. Interreg V-A program of Latvia and Lithuania. The entire project budget is EUR 981,750, of which the general financing of the European Regional Development Fund is EUR 834,490. The management of the Žemaitija National Park is responsible for the content of this mobile application. Under no circumstances can the mobile application be considered to reflect the opinion of the European Union.