NEW YORK ( TheStreet) -- Searching for income, investors have been pouring cash into high-yield municipal funds, which hold bonds that are rated below-investment grade. According to Morningstar, the tax-free funds yield 4.0%. That is the equivalent of a taxable bond with a yield of more than 6% for someone in the top tax bracket. In comparison, intermediate municipal funds -- which emphasize investment-grade bonds -- deliver tax-free yields of only 1.6%.While low-quality municipals can be enticing, they come with considerable risk. During the market turmoil of 2008, high-yield municipal funds lost 25.3%, trailing intermediate funds by 23 percentage points. Because of the big losses, the high-yield funds rank as the worst-performing municipal category for the past five years. Follow TheStreet on Twitter and become a fan on Facebook. To get decent income without taking on much risk, many investors should consider those investment-grade funds that deliver above-average yields. The funds fatten their yields by holding big stakes in bonds rated A and BBB, the two lowest rankings in the investment-grade universe. This strategy is different from the approach of typical investment-grade portfolios, which steer away from BBB bonds and focus on issues that are rated AAA and AA, the top two categories. While they yield 2 percentage points more than top-rated AAA issues, the BBB bonds have tiny default rates. Defaults should remain limited because many municipalities have reduced budget deficits in recent years by cutting payrolls and raising taxes. Intermediate funds with above-average yields and strong long-term performance records include BlackRock Intermediate Municipal ( MEMTX), Commerce National Tax-Free Intermediate Bond ( CFNLX), USAA Tax Exempt Intermediate-Term ( USATX), and Vanguard High-Yield Tax-Exempt ( VWAHX). A steady choice is USAA Tax Exempt Intermediate-Term, which yields 2.5%. During the past 10 years, USAA returned 5.0% annually, outdoing 85% of intermediate competitors. While the average intermediate fund has 63% of assets in bonds rated AA or AAA, USAA only has 32% in the top two grades. The average fund has 8% of assets in BBB bonds, compared to 27% for USAA. "We manage our fund with an income focus, and a lot of times we have the highest yield available in the intermediate-term category," says portfolio manager Regina Shafer.