A major drought along the lower Danube has highlighted the river\'s reduced ability to buffer extreme weather events and has hampered navigation, environmental group WWF said on Tuesday. The Danube is currently seeing its lowest levels since 2003, with bigger ships often being blocked by multiple sand bars, according to Bulgaria\'s Danube exploration agency. Traffic on the river was disrupted on Tuesday when water levels on a 40 kilometres (25 mile) stretch in Serbia were too low because of lack of rainfall, media said. The WWF said human intervention such as gravel extraction, dredging and dams has contributed to the gradual loss of wetlands that can soak up water during rainy periods and release it slowly during drier times. A WWF bird-watching expedition during the summer found as a result a drastic drop in bird populations along the lower stretch of the river in Bulgaria and Romania. \"The current dry conditions highlight the need to minimize the impact of structural interventions (...) as they reduce the resilience of water ecosystems,\" WWF Danube-Carpathian programme director Andreas Beckmann said. He raised the need to rethink plans for new infrastructure works to eliminate rapids and improve navigation as well as the planned construction of new hydropower stations on the river. According to Beckmann, these may affect the ecological status of freshwater ecosystems along the whole 1,000-kilometre (620-mile) lower stretch of the Danube. Besides, \"the feasibility of hydropower and navigation projects relies on predictable water levels while climate change is expected to lower predictability,\" another WWF expert, Irene Lucius, warned. On Tuesday around 100 ships carrying more than 1,000 tonnes were blocked where the Danube enters Serbia at Bezdan because water levels were 56 centimetres (22 inches) lower than normal, the Beta news agency reported. Around 40 kilometres farther downstream the level is 16 centimetres lower, the agency said. For traffic to resume water levels would have to rise by at least 50 centimetres, an unlikely event in the coming days as no rain is forecast. The Danube, Europe\'s second largest river, originates in Germany and flows through central and eastern Europe before emptying into the Black Sea.