Bad loans held by German banks in the shipping sector remain a concern ahead of the European Central Bank’s stress tests, according to a country review by the International Monetary Fund.

While German banks are “generally well positioned,” lenders holding extensive shipping portfolios “could be a source of further impairments,” the IMF said in the report published today. German banks including Commerzbank AG (CBK), HSH Nordbank AG and NordLB control about one-third of the $475 billion global shipping-finance market in 2012, Moody’s Investors Service said in April.

The three lenders set aside more than 3.6 billion euros ($4.9 billion) for bad shipping debt in the past three years amid a slump in the global sea-freight market. The ECB began auditing 128 banks in February and will conclude in October.

HSH posted a loss of 814 million euros last year, its biggest since 2008, as it provisioned more funds to cover risky loans. The bank, based in Hamburg and the northern city of Kiel, said in April it expects a profit before and after tax as risk provisions will be lower than in 2013.