PENGARUH KEGIATAN WISATA TERHADAP KUALITAS AIR SUNGAI SIBIRU BIRU KECAMATAN BIRU-BIRU KABUPATEN DELI SERDANG Effect of Tourist Activities on Water Quality In Sibiru Biru River District of Biru-Biru Regency of Deli Serdang - Hikmah, Rawiyatul (Program Studi Manajemen Sumberdaya Perairan, Fakultas Pertanian Universitas Sumatera Utara, 2015)