3.1. Overview

      Law number 6 of 1996 concerning Indonesian Waters classifies inland waters into rivers, lakes, reservoirs, swamps, and other bodies of water. The fish management area in the Indonesian Republic for catching and/or growing the fish carried out in the territorial waters. It includes the Indonesian Exclusive Economic Zone (EEZ) and the inland waters area stipulated in Law Number 31 of 2004 concerning fishery as amended by Law of the Indonesian Republic Number 45 of 2009. Indonesia's inland waters consist of around 5,590 main rivers with a total of 94,573 km and around 65,017 tributaries, around 840 lakes and 735 lakes (small lakes), and 162 reservoirs (Depkimpraswil, 2003). In calculating those ecosystems, the area of ​​inland water bodies reaches 19.7 million ha. The total inland water area, 65%, is in Kalimantan, 23% in Sumatra, 7.8% in Papua, 3.5% in Sulawesi, and 0.7% in Java, Bali, and Nusa Tenggara. (Sarnita, 1986; Kartamihardja, 2005).

The latest study on the number of lakes in Indonesia shows 5,807 lakes spread across five major islands (LIPI, 2020). The classification of lakes in the study includes all types of lakes (oxbow, rain-drained lakes, artificial, and others.) as well as dams, swamps, lakes, and reservoirs. These lakes are classified into five categories, namely: 1) very large (> 100,000 ha), a total of 1 lake; 2) large (10,000 - 100,000 ha), a total of 7 lakes; 3) medium (1,000 - 10,000 ha) a total of 38 lakes, 4) small (1 - 1,000 ha) a total of 3,281 lakes, 5) very small (< 1 ha) a total of 1,512 lakes. Kalimantan is the island that has the most lakes, followed by Java-Bali-Nusa Tenggara, Sulawesi, and Sumatra Island, and the island with the least number of lakes is Maluku- Papua.

Rivers, according to Government Regulation No. 38 of 2011 concerning rivers, are natural and/or artificial water channels or containers in the form of a water drainage network, and the water in it, starting from the upstream to the estuary, bounded on the right and left by a demarcation line. The river recorded in the territory of Indonesia is around 5,590 main rivers and 65,017 tributaries, with a total length of the main rivers of 94,573 km and an area of ​​watersheds reaching 1,512,466 km2 (Depkimpraswil, 2003; KLHK, 2021). Based on the classification of length by Sunaryo et al. (2004), river waters in Indonesia consist of a length of >400 km (15 units), 200 – 399 km (27 units), 100 – 199 km (80 units), 50 -99 km (208 pieces) and length < 50 km (5,260 pieces), with a total of 5,590 rivers.