Complex sentence: Kihon Keikaku (2007) Sewage from Rikuzen Takada city had been discharged into nearby waterways which fed into the lake, but in 1998, the city constructed a new system for treatment of sewage.
Split into simpler sentences: Kihon Keikaku (2007) Sewerage from Rikuzen Takada city had discharged into nearby waterways which fed into the lake. In 1998, the city constructed a new system for treatment of sewage.