Glossary

The words you meet at the lake, on the coast and in tide tables.

Accuracy: Our measure of how well the calculation hits at a gauge, in minutes. We hold back the last five days of measurements, calculate without them, and then compare with what was actually measured. The value is shown at every tidal spot — it is measured, not claimed.
Bathing season: The period in which monitoring takes place — in Germany usually mid-May to mid-September. Outside it no samples are taken, and many municipalities apply different rules then, for dogs for instance.
Bathing water: A body of water where many people swim and which the authorities therefore monitor. The term is not a description but a legal status: only where it applies are there water samples and a classification.
Blue-green algae: Actually cyanobacteria, not algae. In warmth and with surplus nutrients they multiply en masse and turn the water a murky green; some kinds produce toxins. The most common reason for a bathing warning at lakes. Recognisable when you can no longer see your feet in knee-deep water.
Bodden and fjord-like inlets: Shallow Baltic coastal waters reaching far inland — “Bodden” on the Western Pomeranian coast, “Förden” in Schleswig-Holstein and Denmark. The water is brackish, warmer than the open Baltic, and its level follows the wind, not the tide.
Brackish water: A mixture of fresh and salt water, as in river mouths, Bodden and the western Baltic. Less salty than seawater, hence different animals and plants — and a different feel when swimming.
Chart datum: Abbreviated SKN, the reference surface of nautical charts and the official tide tables. It lies so low that the water practically never falls below it — the safe assumption for shipping. That is why larger numbers stand there than with us.
Classification: The verdict on a bathing water: excellent, good, sufficient or poor. It is produced from the measurements of four bathing seasons together, so it speaks about the past, not about today.
Dog beach: A stretch of beach where dogs are explicitly allowed — usually a separate area, because they are banned from the main beach during the bathing season. Whether leads are required is on the sign on site.
E. coli and enterococci: Two groups of bacteria from the gut of humans and animals. They rarely cause illness themselves, but they are easy to measure and indicate that faeces have entered the water — and with them possibly pathogens that do cause illness.
EU Bathing Water Directive: The European rule under which bathing waters are regularly tested for intestinal bacteria during the bathing season and sorted into four classes. Each country reports its results to the European Environment Agency — that is where our register of monitored spots comes from.
Gauge: The station where the water level is recorded. Every swimming spot inherits the times of the nearest suitable gauge; if it is further away, a note says so.
Gauge zero: The zero point of a single gauge. Historically placed so the readings never go negative. It applies to that one gauge only.
German datum (NHN): Abbreviated NHN, the official height reference surface in Germany — the zero on maps and town signs. Our default display.
High tide: The highest level of a tide, the point where the water stops rising. Not to be confused with river flooding, which in German shares the same word.
Incoming water: The time between low and high tide, the water is rising. Seafarers call it the flood — meaning the movement, not the peak.
Lido: The Italian word for beach or shoreline, from Latin litus, “shore”. The Lido of Venice carried it into other languages: in Britain and Australia a public open-air pool is still called a lido, in Italy also a managed stretch of beach. We took it as our name because it means the same thing in many languages: the place where you go into the water.
Low tide: The lowest level of a tide, before the water rises again.
Mean water: The average of all water levels at a place. Shows most vividly how far the water swings above and below the middle.
Mudflats: The seabed that falls dry at low tide. The North Sea Wadden Sea is a national park and World Heritage Site.
Natural pool: A pool with built basins but no chlorine: cleaning happens via planted filter zones. Between an outdoor pool and a swimming lake, and run as one or the other depending on the municipality.
Neap tide: The counterpart: the weakest tides at half moon, when sun and moon stand at right angles.
Not monitored: Our label for bathing places that are not covered by the EU directive: no sampling plan, no classification. Usually local people entered them in OpenStreetMap. Where a spot is listed by an authority but not sampled, we write “official, not sampled” — the same state of knowledge about the water, but a different origin. Untested is not the same as dangerous — we simply cannot say anything about the water there.
Nudist: “Freikörperkultur” — bathing without swimwear. On the German coast and at many lakes there are designated sections for it; we list them as separate swimming spots because they are their own areas next to the main beach.
Outdoor and indoor pools: Pools with built basins and supervision. They are not covered by the Bathing Water Directive but monitored by the operator under separate rules. So instead of an EU classification, their pages show what you need before the trip: opening hours, address, phone number.
Outgoing water: The time between high and low tide, the water is falling. Seafarers call it the ebb.
Spring tide: The especially large tides at full and new moon, when sun and moon line up and their effects add. Roughly every 14 days.
Swimming banned: The strongest official measure: swimming is prohibited. Weaker are “swimming not advised” and a plain warning — there you decide yourself but carry the risk. “Under investigation” means a finding is still being checked.
Swimming lake: A still inland water for swimming. Often a former gravel or sand pit filled with groundwater. Such lakes are usually deep, cold, and have steep underwater edges.
Teaching pool: A small, shallow, warm basin where swimming is taught. Usually attached to a school or gym and open to the public only at certain times.
Tidal constituents: The base oscillations a tide is composed of — each belongs to a movement of moon or sun. From a gauge’s measurement series we determine how strong and how shifted each of them is there, and can then calculate arbitrarily far ahead.
Tidal creek: A channel in the mudflats where the water drains and first returns. Creeks fill earlier than the flats beside them — the reason mudflat walks without local knowledge are dangerous.
Tidal range: The height difference between high and low tide. On the German North Sea coast about 2 to 4 metres depending on the place; in Husum around 3.6 metres. On the Baltic only a few centimetres remain — which is why we show no tide times there.
Tide: The regular rise and fall of the sea. On the North Sea twice a day, more precisely every 12 hours and 25 minutes.
Wind surge: The share of the water level caused by wind and air pressure. Onshore wind pushes extra water towards the coast, offshore wind pulls it out. In a storm that is more than a metre and over half an hour of time shift. Wind surge cannot be calculated months ahead — it is weather, not astronomy.