It has been suggested that in tropical lakes, anoxic depth is a more effective
measure of mixing depth (Melack 1978). When thermoclines are complex as they are in Lake Challa, it may not be clear which are transient and which represent the boundary of persistent mixing. Comparing the changes in temperature with changes in selected chemical components can sometimes help to identify the recently mixed zone (Wood et al. 1984). In Lake Challa, a weak thermal stratification in September was still accompanied by a strong oxygen decline, which is typical of many tropical lakes (Baxter et al. 1965; Corbet et al. 1974; Melack 1978; Talling and Lemoalle 1998; Schabetsberger 2004).