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Survey of the Moeris Basin from the late 19th century

Lake Moeris is an ancient lake in the northwest of the Faiyum Oasis, 80 km (50 miles) southwest of Cairo, Egypt. It remains today as a smaller lake called Birket Qarun. The lake's surface is 140 ft (43 m) below sea-level, and covers about 78 mile² (200 km²).

Lake Moeris was freshwater in prehistory but is today a saltwater lake. It is a source for tilapia and other fish for the local area. Its area is estimated to varry between 490 mi² (1,270 km²) and 1,700 km² (656 sq. miles).

When the Mediterranean Sea was a hot dry hollow near the end of the Messinian Salinity Crisis in the late Miocene, Faiyum was a dry hollow, and the Nile flowed past it at the bottom of a canyon 2400 m deep or more (where Cairo is located today). After the Mediterranean reflooded at the end of the Miocene, the Nile canyon became an arm of the sea reaching inland further than Aswan. Over geological time that sea arm gradually filled with silt and became the Nile valley.

Eventually the Nile valley bed silted up high enough to let the Nile in flood overflow into the Faiyum hollow and make a lake in it. The lake is first recorded from about 3000 BC, around the time of Menes (Narmer). However, for the most part it would only be filled with high flood waters. The lake was bordered by neolithic settlements, and the town of Crocodilopolis grew up on the south where the higher ground created a ridge.

In 2300 BC, the waterway from the Nile to the natural lake was widened and deepened to make a canal which is now known as the Bahr Yussef. This canal fed into the lake. This was meant to serve three purposes: control the flooding of the Nile, regulate the water level of the Nile during dry seasons, and serve the surrounding area with irrigation. There is evidence of ancient Egyptian pharaohs of the twelfth dynasty using the natural lake of Faiyum as a reservoir to store surpluses of water for use during the dry periods. The immense waterworks undertaken by the ancient Egyptian pharaohs of the twelfth dynasty to transform the lake into a huge water reservoir gave the impression that the lake itself was an artificial excavation, as reported by classic geographers and travellers ^[1]. The lake was eventually abandoned due to the nearest branch of the Nile dwindling in size from 230 BC.

mer-wer (Moeris) in hieroglyphs

The name "Moeris" is a Greek adaptation of ancient Egyptian Mer-Wer (= "The Great Lake").^[2] In ancient Egypt, the lake was also variously called "the Lake", "the Pure Lake", and "the Lake of Osiris". During the Middle Kingdom, the whole area around the lake was often referred to as Mer-Wer as well. Similarly, the Late Egyptian word "Faiyum" (the Sea) came to be used as a reference for the entire region in later times.

• Faiyum Oasis
• Faiyum Governorate
• Faiyum
• Bahr Yussef

1. ^ http://www.newadvent.org/cathen/05329b.htm
2. ^ [1]

• The Hydraulics of Open Channel Flow: An Introduction

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

Coordinates: 29°27′13″N, 30°34′51″E