To determine the declining production of migratory fishes (milkfish, mullet, snapper, jacks) in Naujan Lake, environmental assessment of Butas River is being conducted. Water quality is being monitored and fish samples were collected once a month from April to December 2003. Four stations were considered: Station 1 with Barangay Melgar A; Station 2, Barangay Concepcion; Station 3, Barangay Dao; and Station 4, Barangay Bayani. Water temperature, pH, transparency, dissolved oxygen, and water depth were determined in-situ. Gill net or pante was used in collecting fish samples. Results show that water parameters are not significantly different between stations except water depth. Stations 2 and 3 (mid portion of the river) are relatively low compared to Stations 1 and 4. Migratory fishes collected are mullet, milkfish, and caranx in Stations 1 and 4. Water depth in the mid portion of Butas River is decreasing as a result of heavy sediment disposition. Siltation could be attributed to erosion and other activities like farming and construction of road along Butas River. Migratory fishes in Naujan Lake are considered endangered due to overfishing, introduction of exotic species, and construction of fish corral. Dredging Butas River is recommended to descend migratory fishes from Naujan Lake to Mindoro/ Tablas Strait and ascend from sea to lake. Dredging the river will increase its productivity as it has been noted that no ecological disturbance would occur during dredging. There is also a need to strictly implement Fisheries Administrative Order 217 Series of 2001 Obstruction to Defined Migratory Paths by the Local Government to protect migratory fishes in Naujan Lake.

Lake Mainit, located in northeastern Mindanao, is the fourth largest lake in the Philippines. Its limnology and water quality parameters, however, are not yet thoroughly understood. This study has been conducted to obtain the bathymetry, the vertical temperature-dissolved oxygen profile, and the vertical variations of nutrients in the lake basin including those coming from river tributaries. The bacterial load profile of certain areas has also been studied to determine the levels of coliform bacterial contamination in the lake water. The bathymetric profile of Lake Mainit indicates that the shallowest portions are in the north and south ends of the lake. These portions become progressively deeper towards the center at over 200 m. Maximum depth recorded is 218.75 m. Steep slope dropping off sharply towards the 200-m depth is found at the western coast of the lake along the Malimono Ridge while the eastern coast has a gently sloping profile. The vertical temperature profile of the lake ranges between 26.55°C - 30.00°C with the thermocline layer being observed between 10 m to 40 m. Variations in vertical temperature have been observed at 0 m down to a depth of 30 m. Beyond this depth, variations are minimal ranging between 0.03°C - 0.15°C. The dissolved oxygen concentration at the epilimnion ranges between 7.31 - 7.67 mgOL^-1. Below the thermocline, it rapidly decreases to <2 mgOL-^-1 from 50 m down to the 200-m depth. The oxycline has been observed between 10 m - 40 m. The vertical nutrient profile shows a uniform NH₃-N concentration from 0 m - 60 m which significantly increases at 80 m to 200 m. A decreasing trend in the NO₃-N profile has been observed between 0 m to 30 m which then increases at 60 m to 200 m. Phosphate concentrations are relatively low at 0 m - 40 m. Nutrient measurements from 14 river tributaries show high concentration levels with sources coming from predominantly agricultural lands and residential areas. Bacteriological analyses of water samples coming from 12 sampling stations show high total and fecal coliform (350 to 1600 MPN/100 ml) in the three populated areas around the lake. The study indicates that Lake Mainit is an oligotrophic lake based on its physico-chemical and morphometric characteristics. However, natural productivity and optical properties of the lake waters should also be considered in determining its classification.

Lake Duminagat is a crater lake located in Mt. Malindang Natural Park, one of the protected areas in the Philippines. Two communities are adjacent to it - Brgy. Duminagat, of which it is a part, and Brgy. Gandawan. Both barangays are part of the municipality of Don Victoriano, province of Misamis Occidental. The municipality of Don Victoriano is entirely circumscribed by the Park which represents the flora and fauna of the Zamboanga biogeographic zone. This paper focuses on the objective of characterizing the limnology of Lake Duminagat - its morphology, its physico-chemical components and its biota. The area of study consists of valleys and mountains. Brgy. Gandawan, Brgy. Lake Duminagat, and the lake basin are considered as crater valleys, surrounded by variably tall mountains. Being at a high elevation (~1,240 to 1,560 masl), the climate in the Lake Duminagat area is cooler compared to the lowlands. The area belongs to the region classified as Intermediate B type with no very pronounced maximum rain period and no dry season. Annual rainfall is 2099 mm. Lake Duminagat is a small lake, with an area of 8.04 ha, maximum depth of 20.95 m, water volume of 933,000 m3, mean depth of 11.6 m, shoreline length of 1,060 m, and shoreline development of 1.054. It is a thermally stratified lake, though whether it undergoes periodic mixing was not determined. The water is low in alkalinity and is very soft. The water at the middle of the lake is potable enough for drinking at various times of measurement. Its various morphometric and physico-chemical characteristics such as a low surface area to volume ratio, low lake area to watershed area ratio, low alkalinity, and low amount of dissolved solids all contribute to its low productivity. Its macrophytes (representing one component of primary productivity) and zooplankton (representing secondary productivity) populations are thus low in numbers, aside from being limited in number of species. Consequently, the fish population, which is at the top of the aquatic food chain, is also low in kind, numbers, and biomass. Nonetheless, the lake supports a high diversity of indigenous shoreline fauna and flora. Considering the lake s characteristics and that of its surrounding community, one potential for the Lake Duminagat area is its use for ecotourism with the local people being the hosts-entrepreneurs. The project, of which this paper is a part, was one of the projects in the Philippines-Netherlands Biodiversity Research Programme for Development: Focus on Mt. Malindang and Environs (shortened as BRP). The project used participatory approaches and involved the community as local researchers or partners. It is hoped that their involvement in this research gave the local communities an awareness of the natural and social factors that determine/affect the Lake Duminagat ecosystem. It is also hoped that results of this research would be used and would empower the local communities to come up with a strategy for conserving and sustainably utilizing the lake s biodiversity and resources, and improve livelihood and cultural opportunities.