A pair of actively managed rivals to BKLN debuted last year, each quickly gaining assets. The SPDR Blackstone/GSO Senior Loan ETF (NYSEArca: SRLN) is just 11 months old and already has $616.5 million in assets. First Trust Senior Loan Fund (NasdaqGM: FTSL) debuted in early May 2013 and has nearly $164 million in assets. [New ETFs Off to Fast Starts]

Some investors have questioned the liquidity of the bank loan market.  Others have warned that the trading rate risk for higher credit risk is not worth it because bank loans would be vulnerable in the event of a U.S. recession.

That has not stopped cash from pouring into these funds. Retail inflow to loan mutual funds for 2014 was $4.6 billion as of Feb. 20, Bloomberg reported, citing Bank of America.

PowerShares Senior Loan Portfolio

ETF Trends editorial team contributed to this post.