The Marine Life Information Network

Information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Tidal strength (water flow)

The horizontal movement of water associated with meteorological, oceanographical and topographical factors. High water flow rates result in areas where water is forced through or over restrictions for example narrows or around protruding offshore rocks. Tidal streams are associated with the rise and fall of the tide whereas currents are defined as residual flow after the tidal element is removed (McLeod, 1996).

Rank Water flow rate
Very strong > 6 knots ( >3 m/sec.)
Strong 3 to 6 knots (1.5-3 m/sec.)
Moderately strong 1 to 3 knots (0.5-1.5 m/sec.)
Weak < 1 knot (<0.5 m/sec.)
Very weak negligible


McLeod, C.R., 1996. Glossary of marine ecological terms, acronyms and abbreviations used in MNCR work. In Marine Nature Conservation Review: rationale and methods, (Ed. K. Hiscock), Appendix 1, pp. 93-110. Peterborough: Joint Nature Conservation Committee. [Coasts and seas of the United Kingdom, MNCR Series].