The dive conditions at Aliwal can be both unpredictable and mysterious. There are some guidelines but many factors interacting in a complex manner make it impossible to give any absolute predictions for dive conditions. Not knowing what to expect in this dynamic, forever-changing environment adds an element of excitement, adventure and surprise to a dive and this is the secret to Aliwal Shoal and her many mysteries.

Currents

Currents are a major factor in determining dive conditions as they may affect water temperature, speed and direction of drift and visibility. Aliwal is dived as a drift dive, with the exception of the wrecks.

The currents on Aliwal are dynamic and unpredictable. They generally flow along the reef in a northeast / southwest axis, parallel to the shore and vary in strength from non-existent to very strong. Directional changes are influenced by many factors including wind direction, onshore-offshore meanders of the Agulhas current and inshore circular currents.

The Agulhus Current

The east coast of South Africa is under the constant influence of the mighty Agulhas current. The Agulhas has a main stream about 60km wide and can move at speeds of up to 5 knots (9.25km per hour). This current is responsible for bringing in warm, clear tropical waters as it flows just like a river down the African East coast. Although these waters are low in nutrients, they carry a great diversity of species from the tropics. The shelf of KZN is one of the narrowest found off Southern Africa and narrows to about 15km off the Aliwal area. Aliwal Shoal lies some 5km offshore and is thus strongly influenced by the Agulhas, which flows along the continental margin.

Winds

Currents inshore of the Agulhas are thought to be predominantly driven by wind and during wind free periods the current may be slack for days. North-easterly winds drive south-westward currents and south-westerly winds drive north-eastward currents (winds are described from the direction from which they come, whereas currents are described from the direction to which they flow). These wind driven currents tend to be stronger near the surface.

Visibility

Visibility can change quickly and ranges from almost nothing to a crystal clear 30m plus.

Visibility may be reduced by heavy rains (mostly in summer) leading to run-off from the Umkomaas River and disturbed bottom sediment due to large swells causing surge. If there is no current and unclear water, it tends to “sit” on the Shoal. A south-westerly wind usually clears up the water as it pushes warm, clean surface Agulhas water inshore, whereas the north easterlies push inshore surface waters offshore, resulting in upwellings of cold, greenish, unclear waters.

Surface Conditions

Since the reef lies 5km out to sea, in relatively shallow water and parallel to the coast, it is exposed to the impact of stormy seas.

At times when exceptionally large swells are encountered (usually after a winter “cold front”, they may, on occasion, be seen breaking spectacularly on Aliwal. These large swells affect dive conditions by causing surge, which is worse at shallower depths. It is best then to stay on the deeper sections of the reef and well away from the shallow pinnacles.

Surf can sometimes get too rough to launch. This is largely influenced by wind. An offshore breeze has a smoothing effect on the ocean while onshore or easterly winds result in messy, choppy conditions with waves that are difficult to time. A launch through large swells that are smooth and consistent is often easier than that through small but messy waves.

Sea Temperatures

Temperatures may reach 27ºC in summer and winter temperatures are usually quite mild at around 21ºC.

Surface inshore water is warmed by the strong sunshine in summer, this warming effect is reduced in winter and the water temperature drops. Winds also affect water temperatures. South-westerly winds lead to warmer waters and north-easterly winds blow surface water offshore and result in colder, deeper offshore waters moving in to replace these waters.

Equipment Suggestions

For winter diving, a minimum of a 5mm full wetsuit is suggested. For those that suffer the cold, a hood is also recommended. For summer diving, a 3mm suit or even a shortie may be adequate but if you feel the cold rather stick with a 5mm.

Weather

Rain, wind and sunshine obviously affect dive conditions and different seasons have a marked influence on weather conditions. KZN has a subtropical climate. Summer is hot and humid with plenty of sunshine but frequent thunder storms and 70% of the annual rainfall. Winter is generally dry and mild. Cold fronts lasting typically three to five days are more frequent in the winter months and bring an invasion of cold air up from the south and southwest. Spring tends to be unsettled with unpleasant winds. Autumn is preferable with little wind and warm temperatures.