Japanese Banks at $1 Trillion RiskFILE PHOTO: U.S. Dollar and Japan Yen notes are seen in this picture illustration June 2, 2017. REUTERS/Thomas White/Illustration/File Photo

A global banking watchdog is warning that Japanese banks are facing a growing risk because they have more than doubled the amount of U.S. dollars borrowed from overseas.

According the Nikkei Asian Review, data from the Bank for International Settlements shows the banks’ dollar assets have grown to about $1 trillion since before 2008. That leaves them with about $3.5 trillion in assets, with $2.5 trillion in dollar liabilities. The data doesn’t include the amount of assets the banks might hold in other currencies.

The driving force behind the growth is the extremely low interest rates in the island nation, forcing banks to riskier overseas opportunities paying higher yields says the Bank of Japan.

Because the banks borrow in a short-term basis, like currency swaps, to pay for their investment it increases rollover risks and that can result in more interest owed. The real risk comes if a credit crisis, like the one in 2008, hits the market, making it difficult to secure dollar funding.