https://geoserver.lounaistieto.fi/geoserver/ymparisto/ows?SERVICE=WMS&

From the dataset abstract

The file contains data on submerged macrophytes in shallow inlets along the Swedish and Finnish Baltic Sea coast (excluding the Botninan Bay, the Quark and southern Scania County). The data was compiled and analysed by Joakim Hansen (Stockholm University) during the project NANNUT (European Regional Development Fund, Central Baltic Interreg IVa, Archipelago and Islands). Macrophyte surveys were conducted in late July to early September 2001–2010 using the method of Persson & Johansson (2007. Manual för basinventering av marina habitat [1150, 1160 och 1650]. Metoder för kartering av undervattensvegetation, version 5. Swedish environmental protection agency [In Swedish]). Values are averages per inlet and year and are based on a minimum of 3 survey transects. Filamentous algae is expressed as the percentage of survey squares with a high cover of filamentous algae. The other macrophyte groups are expressed as mean percentage cover. Levels should be read as ≥10%<20% (i.e. 10 – 20). Full data is stored in the database 'GRUNDA' (2011).

Source: Shallow inlets - Vegetation and mussel communities 2011