BANGKOK (AP) — Experts say the aquamarine color the Mekong River has recently acquired may beguile tourists but it also indicates a problem caused by upstream dams.

The water usually is a yellowish-brown shade due to the sediment it normally carries downstream. But lately it has been running clear, taking on a blue-green hue that is a reflection of the sky. The water levels have also become unusually low, exposing sandbanks in the middle of the river.

Low water levels pose an obvious problem for fishermen and farmers, but experts say the decline in sediment exposes a different danger that can result in erosion of the river banks.

Conservationists say a large hydroelectric dam upstream in Laos that began operating in October is a major contributor to both problems.