Origin of the Name

• It is unknown where the name “the Red Sea” (Al-Bakhr al-Ahmar) comes from The ancient Greeks called it the Eritrean Sea, a name derived from the Greek word “ethnos” meaning red. Although there are different theories about its origin, it has not yet been resolved which theory is correct. Pre-Christian nations such as the Achaemenids (a Persian pre-Christian empire) assigned colours to the cardinal directions: red symbolized the South, and “the sea in the south” could have been the origin of the “the Red Sea”. Another explanation derives from the red cliffs found in some coastal areas, whose rocks contain a high amount of iron oxide colouring them reddish-brown, thereby perhaps leading to its current name.
• Yet another theory is based on the proliferation of red algae known as Trichodesmium erythraeum, which colours entire coastlines red from time to time when they flower.

Formation

• The Red Sea was formed 38 million years ago—relatively recent in geological terms—by the separation of the African and Asian tectonic plates. Even today, the distance between the two plates increases continuously (0.8 cm per year in the north and 1.6 cm in the south), so in a few million years the Red Sea will have expanded into a considerable ocean. Currently, it has a length of 2,300 km and a width ranging from 30 km at the strait of Bab-el-Mandeb, “the Gate of Tears”, between Yemen and Djibouti, to a maximum of 350 km. Along the coasts, the seafloor falls to a depth of 550 m and drops to over 2,000 m in some places in the middle of the sea. The deepest trench with a depth of about 2,800 m is located near Port Sudan.

• The strait of Bab-el-Mandeb is only about 130 m deep, significantly impeding the circulation of water with the Indian Ocean. Because of this geological characteristic, the Red Sea once dried up completely in the course of the last five million years and almost dried up again during the last ice age 10,000 years ago. It is, therefore, a very young sea, where the flora and fauna had to start from the beginning. The island of Sernaka, for instance, bore witness to large fluctuations in the sea level over thousands of years. Between its rocks lie the remains of many corals, indicating that the island once lay below sea level.
• The barrier in the south of the Red Sea also represents an obstacle for marine life that was overcome by only a few species from the Indian Ocean, thereby also leading many species of fauna in the Red Sea to develop independently from their relatives in other seas. These so-called endemic species are exclusively found there. The limited circulation of water with the Indian Ocean and lack of tributaries lead to further differences to other oceans, which are also reflected in the diving conditions.

Salinity

• In the summer, the amount of water that evaporates over the entire surface of the Red Sea is much higher than the amount of water flowing in through the narrow strait at Bab-el-Mandeb. The sea level drops during this period by up to 0.7 m and rises again during the winter. This enormous evaporation leads to a salinity far higher than in other seas. While the Indian Ocean has a salinity of 3.4%, the Red Sea has an average of 4.1%. This forces us, divers, to carry more weights than usual to compensate for the increased buoyancy.

Underwater Visibility

• Since few nutrients reach the Red Sea through its narrow strait, it has less plankton. In addition, there are no tributaries that would enrich the sea with nutrients. These two factors lead to much better visibility than in other seas—it can easily reach 40 m and beyond at reefs without a sandy seabed.

Water Temperature

• The water temperature is also a peculiarity. Whereas the temperature ranges between 5 to 7° C in other seas, the Red Sea has a temperature of 20° C even at a depth of 1,000 m. It is caused by a trench along the seafloor, formed by plate tectonics, whose volcanic activity heats up the water. The surface temperature lies at an average of 25°C and can easily reach 32° C on the coasts and reef flats during the summer. In the winter, the water at the surface cools down to 19° C in the north, while rarely dropping below 22° C in the south. Thus, the use of a 5 mm wetsuit is sufficient from May to October. Many divers even content themselves with a neoprene shorty as protection against the cold. However, a thicker wetsuit is needed in the colder months from November to May.

Currents and Tides

• High evaporation is the main generator of currents in the Red Sea. In the summer, the concentration of salt at the surface increases, making the water heavier and causing it to sink. Deepwater flows towards the Indian Ocean, and lighter water flows along the surface into the Red Sea. In the winter, the directions are inverted. During the warm season, the currents mainly run from north to south along the coasts and reefs. However, a reef’s topographic features may also alter
• the flow. In addition, currents are also caused by tides. Due to the gravitational pull of the moon and sun, the mass of water rises and falls in 12hour cycles causing the horizontal water movements of the currents. These currents overlap and mix with the general currents thereby affecting the local diving conditions.
• To the north, in the gulfs of Suez and Aqaba, the difference between the high and low sea levels, or tidal range, can reach up to 1.8 m. The tides in the rest of the Red Sea, especially in the South, are relatively weak, with an average of only 0.8 m.
• For divers, this means that we must constantly take chances in the current into account. At the reefs in the middle of the sea (Brothers, Daedalus, Shaab Sharm, etc.), the fluctuations in the intensity and strength of the currents are rather moderate during a dive. On reefs with a shallow seabed (about 20 m or less), this fluctuation is sometimes more noticeable. In addition, turbulence may occur, stirring up the sand from the seabed and reducing visibility.
• Strong currents can at times be caused by the tides flowing between two close reefs, such as at Shaab Marsa Alam with its isolated ergs to the south—the narrower the channel, the stronger the current. If the schedule permits it, dive at these places at low or high tide to take advantage of the time with the least water movement.

Assessing the Current

• The currents’ strength and direction at each reef in each season generally remain the same every year, making them easy to predict. However, do not take them for granted.
• Never assume that the currents always flow in the same direction as the waves on the surface. Furthermore, the currents near the surface may also flow in another direction than those below. When in doubt, always check the current’s direction and strength before diving (current check). To do so, lower a lead weight attached to a rope to a depth of at least five metres, or even a bit deeper. The weight is carried by the current allowing you to detect its direction. However, this method works only with stronger currents. Another option is to observe the fish and soft corals on the reef before descending. Among the fish, the territorial anthias face the incoming current making
• their tails always point in the direction of the current’s flow.
• One difficulty in assessing the current is caused by reefs’ shapes, which either deflect or divert the current. At reefs with steep walls, swirls may form, leading to unexpected countercurrents. If a strong current is present, it is important to always remain close to the reef walls to avoid being swept out into the open sea. If it does happen, release the surface marker buoy as soon as possible and ascend to the surface. The RIB drivers will immediately recognize the problem through the buoy and follow the divers. Trying to fight the current to get back to the reef is always useless.

Climate

• Egypt has a consistently hot and dry climate. The average temperature, depending on the latitude, ranges between 22 and 30° C. The greatest temperature variations are found in the Gulf of Aqaba, where the temperature drops to 15°C in the winter and rises to 45° C in summer.
• However, the temperatures at sea lie slightly below those on the coast. It is also usually windy making the weather rarely uncomfortably hot-it may even get quite chilly in the early morning and evening, so always bring along a light jacket.
• The humidity varies from 60% in the winter to 70% in the summer, and it almost never rains, apart from perhaps a day or two in the winter. For people with allergies, this dry air is a blessing in spring, since there is no pollen in Egypt-divers suffering from pollen allergy can normally enjoy their hobby without problems. However, divers must still get their allergies assessed by a doctor knowledgeable in diving.

Winds

• Because of the monsoon, the winds. come from the north-northeast in the summer and from the southwest in the winter in the Egyptian part of the Red Sea. Windless days are rare. A light breeze with wind speeds of one to three Beaufort blows constantly during the day, while usually diminishing noticeably
• In some situations, the wind increases considerably reaching higher speeds. In general, these stronger winds must be expected during the cool season from October. to May, when storms also occur more frequently. Note however that they may even occur in the warm summer months with wind .speeds reaching up to. nine Beaufort, which can cause mild seasickness in even the most seaworthy divers.
• On and offshore winds that occur on coastal areas due to the fluctuation in temperature during the day are usually of less importance to liveaboard tours since most reefs lie too far off at sea to be affected much by the coastal regions.

Waves

• are caused by the wind blowing over the surface. of the sea with their height, length and .strength depending. on the wind’s speed. Since the movement of air off the. the coast is usually stronger than near the coast, waves at sea are higher, so dive sites such as the Brother Islands are more difficult to dive at. then at the sites near the coast. Also note that the larger the reef is, the more shelter it offers from the waves. Liveaboards always moor on the leeward side of a reef (the side away from the wind) and exclusively moor at reefs and islands that provide sufficient shelter during overnight stays.
• The effects of the waves on, the surface during a dive are hardly noticeable even at a relatively shallow depth. However, they are important for divers during entry and exit, where high waves can lead to many dangers:
• The RIB risks being swept onto the corals .by high waves when it is close to the reef, and they also make it difficult for groups to stay together at the surface. In such cases, it is important to quickly enter the water and descend straight away 
• Similarly, getting back into the RIB at the end of a dive can also be problematic in such conditions. especially at the side of the reef that is exposed to waves where there is a significant risk that the divers will be swept onto the reef flat after surfacing, seriously injuring them.
• Boarding a RIB from a liveaboard can also be problematic in high seas. One way to increase the safety is to bring the diving gear into the RIB beforehand and board it without carrying the load. However, even then good timing is important 

Surge

• Along with the waves comes the surge, the movement of the water below the surface. The rising and falling of the waves are transferred to the water below making it circulate. With sufficient distance to the reef walls and corals, this phenomenon is usually pleasant. However, there is always the danger that divers may get pushed against the rocks and corals of the reef if they do not keep a safe distance.