Fish farming in Egypt is not formally recognized as an agricultural activity, so aquaculture cannot use water from irrigation canals. However, fish are raised as primary or secondary crops in combination with fruit and other plant crops. A study by the WorldFish Center found farms could efficiently use well water to intensively raise tilapia in aerated tanks and use the effluent to irrigate fruit trees, vegetables and flowers. Two other farms used water from nearby Nile irrigation canals to fill water storage reservoirs stocked with tilapia. Crops and fruit were the main source of revenue for these farms, and fish reflected a minor secondary crop.