Which of the following is NOT considered an environmental impact of an irrigation scheme that draws water from a river?

The correct answer is that decreased evaporation in the area is not considered an environmental impact of an irrigation scheme that draws water from a river. In fact, implementing an irrigation scheme typically involves diverting water from its natural flow, which can actually lead to increased evaporation, particularly in areas where water is placed on the surface for crop irrigation.

In contrast, altered water sediment flow refers to how water diversion can change the natural sediment transportation processes in rivers, which can affect river morphology and ecosystems. Reduced groundwater recharge is a significant concern because withdrawing large amounts of water from surface sources can diminish the replenishment of groundwater aquifers, disrupting local hydrology. Similarly, changes in local fish populations can occur as alterations in water flow and temperature affect aquatic habitats, leading to shifts in species composition and abundance.

Therefore, among the options, decreased evaporation does not align with typical consequences of river water extraction for irrigation, making it the correct choice.