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• Metal bioavailability estimated by simple bioavailability extraction test (SBET). • Probabilistic integrated ecological risk assessment method (PIERA) was developed. • PIERA integrated SBET and triangular fuzzy numbers into Hakanson's eco-risk index. • Cd and areas around S2 and S5 was identified to be priority pollutant and areas. • Cd originated from both non-point agricultural and industrial pollution sources. Heavy metals (Cr, Cu, Zn, Pb, Cd) concentrations and fractions in surface sediments from Honghu Lake were detected by an atomic absorption spectrophotometer and Simple Bioavailability Extraction Test (SBET) from 11 typical sites to explore their spatial distribution, bioavailability and sources. Results showed the mean I geo s and ecological risk degrees decreased in the order of Cd>Cu>Cr>Pb>Zn and Cd>Cu>Pb>Cr>Zn. The metals' bioavailability estimated by SBET decreased in the general order of Cu>Pb>Cd>Zn>Cr. Under integrated consideration of metal enrichment, ecological risk and bioavailability, it obviously made the decision-makers confused to identify final priority pollutants and priority areas. Thus, a probabilistic integrated ecological risk assessment method (PIERA) was formulated based on the potential ecological risk index (PER), SBET and triangular fuzzy numbers for synthetically assessing metal enrichment, ecotoxicity and bioavailability. With the help of PIERA, Cd was finally regarded as the risk priority metal due to the integrated potential eco-risk of Cd made the average contribution of 86.4% to the integrated RI s. Moreover, the areas around S5 and S2 were regarded as the risk priority areas. The case application of PIERA revealed that this improved method is of a better resolving ability which scientifically supplies the integrated information of enrichment, bioavailability and systematic uncertainty for decision-makers compared with the other prevalent indexes (SQGs, I geo , PER). The consequence of the Pearson correlation analysis, distribution analysis and field investigation indicated that Cd mainly originated from both non-point agricultural and industrial pollution sources. [ABSTRACT FROM AUTHOR]