Sea level statistics
Sea water level is measured at mareographs (tide gauges) along the Finnish coast. In Finland, the most important factor affecting sea level variations is wind, and extreme sea levels are thus measured during stormy weather. The variations also depend on location. Largest sea level variations occur in the ends of the bays; on the Finnish coast in the Bay of Bothnia and eastern Gulf of Finland. The variations are smallest in the central Baltic Sea, which means in Finland the Sea of Åland and the Archipelago Sea.
30-year statistics
The graphs below present statistics calculated from the sea level observations 1991–2020. The highest and lowest sea water levels from every station and the 30-year averages are presented as solid lines. The averages of the annual maxima and minima 1991-2020 are presented as dashed lines. The highest and lowest annual averages are presented as dotted lines. The values are calculated in two height systems. On the first graph the values are referenced to the theoretical mean water (MW) and on the second to the N2000-system. The N2000 system is based on precision levellings and fixed to land. On the other hand, the height system MW approximately follows the average sea level. The height systems differ from one another as the average sea level changes in relation to fixed land due to e.g. land uplift and global sea level rise.
Extremes
The table below gives sea level extremes measured in Finland referenced to theoretical mean water. The last column tells the year the station has started to measure. When referenced to the theoretical mean water (MW), the extremes mainly consist of variations caused by weather conditions.
| Station | Maximum (date) | Minimum (date) | Since |
| Kemi | +201 cm (22.9.1982) | -128 cm (14.1.2016) | 1922 |
| Oulu | +183 cm (14.1.1984) | -131 cm (14.1.1929) | 1922 |
| Raahe | +162 cm (14.1.1984) | -129 cm (4.10.1936) | 1922 |
| Pietarsaari | +139 cm (14.1.1984) | -113 cm (4.10.1936) | 1922 |
| Vaasa | +144 cm (14.1.1984) | -103 cm (2.1.2019) | 1922 |
| Kaskinen | +148 cm (14.1.1984) | -92 cm (2.1.2019) | 1926 |
| Pori | +132 cm (14.1.1984) | -86 cm (2.1.2019) | 1925 |
| Rauma | +135 cm (22.2.2020) | -80 cm (2.1.2019) | 1933 |
| Turku | +130 cm (9.1.2005) | -74 cm (10.4.1934) | 1922 |
| Föglö | +102 cm (14.1.2007) | -71 cm (10.4.1934) | 1923 |
| Hanko | +133 cm (9.1.2005) | -79 cm (28.1.2010) | 1887 |
| Helsinki | +151 cm (9.1.2005) | -93 cm (28.1.2010) | 1904 |
| Porvoo | +123 cm (6.12.2015) | -69 cm (7.3.2017) | 2014 |
| Hamina | +197 cm (9.1.2005) | -116 cm (20.3.2013) | 1928 |
Referenced to the theoretical mean water
If referenced to other height systems like N2000 (= BSCD2000), the record would tell how high or low the water has been related to the fixed land . As the average sea level slowly changes in relation to the fixed land, such extremes are more time-dependent than those given in relation to the theoretical mean water (MW). Thus, the extremes that have occurred in the past decades might not represent the expected sea level variability of the present day and are not presented here.
29.9.2021