The IJsselmeer, also known as Lake IJssel in English, is a closed-off inland bay in the central Netherlands bordering the provinces of Flevoland, North Holland and Friesland. It covers an area of 1,100 km2 (420 sq mi) with an average depth of 4.5 m (15 ft). The river IJssel, which is what the lake was named after flows into the IJsselmeer.

Friesland, historically and traditionally known as Frisia, named after the Frisians, is a province of the Netherlands located in the country's northern part. It is situated west of Groningen, northwest of Drenthe and Overijssel, north of Flevoland, northeast of North Holland, and south of the Wadden Sea. As of January 2023, the province had a population of about 660,000, and a total area of 5,753 km2 (2,221 sq mi).