Deep-water soloing (DWS), also known as psicobloc, is a form of solo rock climbing that relies solely upon the presence of water at the base of a climb to protect against injury. Participants generally seek high difficulty routes usually above high tide. Although this is viewed as a relatively new style of climbing, it probably originated in the late 1960s or early 1970s in Dorset, Southern England or Majorca. Real development of the style began in the mid-late 1990s, and is progressing to this day.
DWS is remarkable for the traditional style of ascent it ensures, while at the same time being viewed as very modern. Participants are stereotypically very relaxed, occasionally to the point of being thought foolhardy or cavalier by other climbers—however, injuries have generally been very rare. Climbers usually consider the mental aspect of DWS to be comparable to the physical component. Additionally, if a climber falls into the sea below the cliff, he or she must then possess enough strength to swim to safety. This added, and obfuscated, consequence has led to at least one death.
This type of climbing is typically practiced on sea cliffs at high tide, most famously on the coasts of Dorset and Devon, but also in the Calanques near Marseille, around the Southern Pembrokeshire coast, parts of Ireland, Sardinia, Majorca, Spain, Greece, and many other climbing areas.
DWS is occasionally known as water bouldering.
S0 - Safe solo with a good area of deep water.
S1 - Not completely perfect water, with a little care injury is avoidable. Probably highish and worth going around high tide.
S2 - Dangerous routes, possibly necessitating a well aimed fall. The water might not be that deep, or there may be loose rock. High tide is recommended.
S3 - Very dangerous. You may as well be soloing above land, extreme caution should be exercised.
Therefore a climb which has a high difficulty rating could be performed safely should it have a rating of S0 or S1.