This in reply to water hyacinth or water lily comments, yes it true that water hyacinth is an indicator on the quality of water in the lake. The presence of water lily will determine the condition of water. The more water lily, the more polluted is the water. It will hasten the eutrophication process that will deplete the water of dissolved oxygen. The water lilies compete with the aquatic life in the water of dissolved oxygen and generate bacteria causing organisms.
However in Lake Mainit, the situation is different because of its characteristic. Lake Mainit is considered as an oligotrophic lake, so the water lily is not consider a threat in the area. There is also a minimal concentration of this type of plant in fact you can find it only in few places. The presence of water hyacinth in the area will also depend on the season and weather condition. For "Habagat" season its concentration is more on the northern side in Mainit and Alegria, Surigao del Norte while during "Amihan" the water hyacinth is on the southern side in Jabonga, Agusan del Norte. The lake is also deep so that concentration of nutrient will be easily dissolved and settle to 100 meter or more where there is organism that will survive.
Interestingly, during the limnological study there are six areas where hot vents is located because at that point and elevation no temperature is detected, meaning its beyond the thermometer level that is being used. This need further study to confirm the present of hot vent. If there are thermal vent then there is life present or organism that thrive on this particular area. Thermal vents are a hot spring under the water and we cannot deny that the Lake Mainit is surrounded with hot spring. This is also to confirm why Lake Mainit got its name from "Mainit" which means "hot" in Bisaya.
During also the course of study, it found out that the temperature at the mouth of Mainit River will increase during night time. This is at five (5) meter or more below water line. The more you go deep the temperature will increase. Hot vent is found at an average depth of 150 meter below water line on the eastern seaboard of the Lake.