Lake Alaotra lies in the north of Ambatondrazaka (about 250 km north-east of the capital Antananarivo). It is the biggest fresh water lake of Madagascar with a minimum surface area of 22,000 ha of open water. The lake lies in a fosse and is bound by two faults in the crystalline basement, which contains fresh water. The location of its centre point is 17º28'21"S and 48º31'40"E at an altitude of 750 m. The lake is very shallow, fluctuating between 1 and 4 m in depth, and is surrounded by up to 80,000 ha of inundated marsh and irrigated rice fields (especially in the southern and western part).

The climate is tropical semi-humid and is characterized by two alternating seasons. A dry season with moderate temperatures in May - November, and a wet season with elevated temperatures in December - April. The annual precipitation is between 1000 and 4000 mm. An important environmental factor is the high frequency of cyclones passing through this region, especially during mid-January and mid-March, when winds with high speeds reaching 300 km/h and precipitation of 600-700 mm within a few days cause dramatic changes.

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