At least 20 people have died in Serbia and Hercegovina in the Balkans’ worst floods in decades. The River Sava has burst its bank and water levels were still rising Sunday. In Serbia, the power plant that supplies much of the country is threatened in the town of Obrenovac, as thousands of volunteers build flood defenses along the river bank. In Bosnia, landslides have buried houses and floods are affecting Croatia. Serbian tennis champion Novak Djokovic has joined the appeal for help. Israel has sent Belgrade a large consignment of aid.