Few studies of metal pollution in lakes have been carried out in urban environments. This research aimed to determine both temporal and spatial changes in metal concentration in sediments of lakes in London, and identify the current extent of contamination in lake ecosystems as a whole. The novel use of sediment archives to reconstruct potential toxicity was also explored. Sediment cores were taken from seven lakes across London and analysed for Ni, Cu, Zn, As, Pb and Hg concentrations. The cores were dated using a combination of radiometric and SCP dating, and lake age. Temporal trends were found to vary within and between sites, due to metal behaviour, catchment disturbance and the proximity to and type of metal source. PCA showed that there was some evidence for a regional pattern of contamination. Across all sites metal concentrations were very high, exceeding guideline values both in the past and at present. At various times the concentration of Pb had reached levels that were over 2000% higher than the guideline value. Increasing levels of enrichment and flux towards the surface of the cores also showed that contamination was not declining. Metal concentrations were also determined in deposition, water, and biota at one of the lakes. The concentration of Pb was found to exceed guideline values in both water and fish. The extent of Pb contamination in London lakes is therefore a major cause for concern. The potential toxicity of the combination of metals analysed in the sediment cores was reconstructed, through the calculation of mean toxicity quotients. Every core exceeded the potential toxicity threshold at all depths. Comparison to laboratory toxicity test data carried out on sediments from the OPAL lakes showed that the sediments were likely to be toxic, which would have implications for lake ecosystems should they be disturbed.