There are a number of possible explainations:

Answer 1:

This sea is called the "Red Sea" because:

The Red Sea splits into two at its northern end into the Gulf of Suez, and the Gulf of Aqaba. The name originally applied to the Gulf of Aqaba, which bordered the land of Edom, which means "red".

1 Kings 9:26 - And King Solomon made a navy of ships in Eziongeber, which is beside Eloth, on the shore of the Red Sea, in the land of Edom.

Today Eloth is callled Eilat, and is at the north eastern tip of the Gulf of Aqaba, and is located in what was the land of Edom. Esau was born red. Edom, another name for Esau, means "red".

Genesis 25:25 - And the first came out red, all over like an hairy garment; and they called his name Esau.

So the sea that borders the land of Edom is called the Red Sea. It is the Gulf of Aqaba that the Israelites crossed (from Nuweba beach) having walked day and night for six days across the Sinai peninsula. The real Mount Sinai is not in what is now called the Sinai peninsula, but in Arabia.

Galatians 4:25 - For this Agar is Mount Sinai in Arabia.

Source: Bible - Authorized Version

Answer 2:

It is called the Red sea because of a typo in the translation. In Hebrew, it is called Yam Suf (ים סוף) which means "reed sea". An early spelling error caused it to become known as the red sea. Modern Jewish publications are careful to always refer to it now as the Reed Sea or the Sea of Reeds.

Answer 3:

The name of the sea may signify the seasonal blooms of the red-coloured cyanobacteria Trichodesmium erythraeum near the water's surface. Which gives the sea a red coloured look.

See the related Wiki Link for more information:

I have the same problem as I am doing a science project on it at the moment. I believe that the characteristics of the red sea are;

• It is highly salty.
• It is known for dangerous depths as for divers.
• Today, this normally azure-blue body of water fills an extension of the Great Africal Rift Valley, and is over 2000 km long and over 300 km wide at its widest point between Eritrea and Saudi Arabia.

I also believe this about the red sea;

A continental shelf extends from the coast to a maximum distance of 120 km from the port of Massawa, narrowing to about 20 km in the north and south of the country. Its average depth is about 200 metres, and on it lie many low, flat coralline islands such as Dahlak Kebir and Nora, some fewer islands of continental origin such as Howakil and Dissei, and the rare volcanic island of Sanahor. Fringing reefs surround many island, scattered sea grass beds and sandy beaches are widespread, and mangroves line many coasts. These characteristics, in conjunction with a low rate of human settlement on coast and islands, have allowed protected marine species such as sea turtles and dugong to flourish.

Rocky deserts, sand dunes and salt marshes characterise Eritrea's coastline. The coastal plains are very dry and receive only scanty amount of rainfall (less than 200 mm/year). No wonder its population is very small-mostly concentrated on the two ports of Massawa and Assab, with almost the entire fishing communities located in the Dahlak archipelago and on the coastline south of Massawa up to the border with Djibouti, including the islands of Hawakil Bay. Most of the fresh water source is located away from the coast and getting water therefore becomes a major operation involving camels and, in some cases, trucks and boats. Some of the islands are connected to the mainland during low tide, and people then take the chance to walk to the mainland to do chores like fetching water.

The greater wonder, one may think, is why peoples settled here at all.But these are no ordinary people, many of them descendants of ancient mariners who have in the past heeded the call of the deep, and linked the ancient cultures of Africa and Asia across the Red Sea. Many may have originated from the east, from the Arabian peninsula, but a mixed ethnic population resulted from forced migrations due to war, famine, the slave trade, and other exigencies.

The people inhabiting the coastline and Islands include the Afar, Saho, Tigre (Dahalik) and Rashaida. The Afar and Saho people in particular depend on the sea for their lives, being expert fishermen and/or traders in their frail sambuks. On the whole, Eritrea's Red Sea people have maintained their traditional lifestyle of fishing as well as herding goats and camels.

The Afar, for one, are keepers of the ancient art of celestial navigation - they are known to navigate by the night sky without the help of compass, GPS (global positioning system) or any high-tech means of finding location. In ancient times, knowledge of celestial navigation was held as the near-mystical power of a good sailor. The ability to navigated by the night sky implies a strong connection with the natural world, from which many of us have become alienated, as well as our shared past. It only makes per fect sense then that the Afar community actually has a strong tradition of managing their resources through their elders. And that the word "conservation" (dagro) exists in the language, and even better, they have separate terms for "conserve!" (dagursuma) and "let's conserve" (dagurnai).

I hope this helps :)