HAMBURG - Low water levels persist on the Rhine and Danube in Germany and cargo vessels cannot sail fully loaded on the German sections of both rivers, traders said on Monday. The Rhine is too shallow to allow vessels to sail with full loads south of Cologne and Duisburg, traders said. Water levels have been unusually low since early August. The Danube is also too low for ships to sail with full loads along the entire German section of the river, they said. Low water means vessel operators impose surcharges on freight rates, increasing costs for cargo owners. More vessels are needed to transport cargo, also increasing costs. The Rhine is an important shipping route for commodities including grains, minerals, coal and oil products such as heating oil. The Danube is an important route for heating oil and for east European grain exports to west Europe.