The slowest annual growth rate ever reported by the RBA's data on mortgage credit growth - over the year to January - looks to be getting even worse.According to the latest Reserve Bank figures, lenders' total mortgage balances increased by 0.3 per cent in February, compared with the previous month.Balances were up 4.2 per cent over the 12 months to February - the slowest annual growth rate ever reported in the RBA's data series.Owner-occupier balances were up 0.4 per cent over the previous month and up 5.9 per cent over 12 months.There was no growth in investors loan balances, compared with the previous month. Investor balances were up just 0.9 per cent over 12 months.Business credit balances are growing at an annual rate of 5.3 per cent and personal credit balances were down 2.7 per cent over the past year.Australian Prudential Regulation Authority figures indicate even lower growth in the mortgage market. It says lenders' balances grew by only 3.6 per cent over the 12 months to February.Lenders whose books are growing above system over the past year include Greater Bank, Heritage Bank, HSBC Bank Australia, ING Australia, Bank of Sydney, Macquarie Bank, Suncorp, Teachers Mutual Bank and WestpacThose that are growing below system include ANZ, whose aggregate mortgage balance declined 0.1 per cent over 12 months, Bank of Queensland, Commonwealth Bank, ME Bank and NAB.