Since 1873 temperature and salinity of the surface water are monitored at the Helgoland Roads station "Kabeltonne" (54°11.3′N, 7°54.0′E) on every workday usually before 9 a.m. The sampling was extended by dissolved inorganic nitrogen species and phosphate in 1962, dissolved inorganic silicate in 1966, Secchi depth in 1968, chlorophyll a in 2004 and pH and oxygen in 2011. A description of the methodology of each parameter can be found in the Helgoland Roads method guide. Meta-information on specific adjustments to protocols, details about calibrations and maintenance of devices, specific limitations of datasets and further documentation are also provided for each parameter in the section "Documentation" of this collection.