The Zuiderzee (/ˌzaɪdər ˈzeɪ/; Dutch: Zuiderzee, Dutch: [ˌzœy̆dərˈzeː]; old spelling Zuyderzee) was a shallow bay of the North Sea in the northwest of the Netherlands, extending about 100 km (60 miles) inland and at most 50 km (30 miles) wide, with an overall depth of about 4 to 5 metres (13–16 feet) and a coastline of about 300 km (200 miles). It covered 5,000 km² (1,900 sq mi). Its name means "southern sea" in Dutch, indicating that the origin of the name can be found in Friesland to the north of the Zuiderzee (also see North Sea). In the 20th century the majority of the Zuiderzee was closed off from the North Sea (leaving the mouth of the inlet to become part of the Wadden Sea) and the salt water inlet changed into a fresh water lake called the IJsselmeer (IJssel Lake) after the river that drains into it, and by means of drainage and polders, an area of some 1,500 km² (580 sq mi) was reclaimed as land. This land eventually became the province of Flevoland, with a population of nearly 400,000 (2011).

Cornelis 'Kees' Dopper (7 February 1870, Stadskanaal – 19 September 1939, Amsterdam) was a Dutch composer, conductor and teacher.

Dopper's reputation as a composer has suffered from the accusation of being 'too German' for much of his career, and still haunts him to this day. Very popular with concert audiences, his works never received much critical acclaim in his home country (unlike abroad). His reputation among the musical avant-garde further suffered because of the so-called 'Vermeulen incident' of November 1918. After a performance of Dopper's Seventh Symphony (which ends with a march) under the baton of the composer, his dissatisfied colleague Matthijs Vermeulen stood up in the hall of the Concertgebouw and shouted: "Leve Sousa" ("Long live Sousa"); the implication being that Dopper was of little more value as a composer than the critically reviled American marchsmith John Philip Sousa (1854–1932). This caused uproar, not just because of Vermeulen's affront, but also because a great part of the audience understood it to be "Long live Troelstra!" (the name of the socialist leader who'd attempted to unleash a revolution days before), and therefore as a call to revolution. In the aftermath, Vermeulen was banned from attending the Concertgebouw for one week, but the subsequent scandal also caused the orchestra board to 'relegate' Dopper. Dopper died in 1939 and was buried at Zorgvlied cemetery.