Investors have pumped nearly $2 billion into the largest ETF for bank loans so far this year as they hunt for high-yield options that provide some shelter from higher interest rates.

PowerShares Senior Loan Portfolio (NYSEArca: BKLN) has surged to $3.4 billion in assets and is currently paying a distribution yield of 4.6%. For comparison, U.S. 10-year Treasury notes are yielding only 1.7%.

BKLN competes with the index-based Highland/iBoxx Senior Loan ETF (NYSEArca: SNLN), as well as the newer SPDR Blackstone/GSO Senior Loan ETF (NYSEArca: SRLN), which is actively managed. State Street (NYSE: STT) developed the active ETF along with GSO Capital Partners LP, the global credit business of private equity giant Blackstone Group (NYSE: BX). [Senior Loan ETFs Face New Actively Managed Rival]

Trading volume in the bank loan ETFs has been rising of late and BKLN saw “heavy inflows” on Tuesday, according to Chris Hempstead, director of ETF execution services at WallachBeth Capital LLC.

The senior loan ETFs “are all very liquid and each is unique in its own right,” he added.

BKLN, the biggest ETF in the category, has seen its assets more than double since the start of the year, Bloomberg News reports.