Onondaga Creek is a major tributary of Onondaga Lake. The headwaters of Onondaga Creek originate 44 km south of the city of Syracuse, NY near Vesper, NY. Onondaga Creek drains a 298 km2 watershed of mixed land use (~80% forest, rural, and agriculture and ~20% urban) and flows north through the Tully Valley where it enters Onondaga Lake within the city of Syracuse. The major tributaries to Onondaga Creek are the West Branch of Onondaga Creek, Hemlock Creek, and Rattlesnake Gulf. A flood control dam and reservoir constructed by the Army Corp. of Engineers in the late 1940's located within the Onondaga Nation Reservation regulates the peak flow that reaches the City. This structure influences the stream's flow pattern only for large runoff events. Accordingly, a portion of the very high flow is diverted into the reservoir during these intervals and then released back into the stream during recession. Annually, Onondaga Creek contributes approximately 30 % of the hydrological input to the lake, and water quality in the creek has been a concern historically with regards to its impacts on Onondaga Lake. At its mouth, Onondaga Creek is enriched with nutrients and suspended sediment. These problems are enhanced at high flows. Also near the mouth, groundwater springs continuously discharge brackish (salty) water to the creek. Therefore, Onondaga Creek is enriched with salt, as well. A sediment loading analysis in the early 1990's showed that 57 % of the sediment load reaching Onondaga Lake was delivered by Onondaga Creek, although a more recent study has shown that this may have actually been an underestimate. Thus, Onondaga Creek is the largest source of sediment to Onondaga Lake. In addition, approximately 40 combined sewer overflow structures (CSOs) within the city discharge untreated domestic waste directly to Onondaga Creek during runoff events. As a result, Onondaga Creek is the largest source of fecal coliform bacteria to Onondaga Lake, as well. Onondaga Creek is unusual due to the presence of hydrogeologic point sources of suspended solids located 33 km upstream from Onondaga Lake. These hydrogeologic structures are termed "mudboils". Mudboils represent the effusion of soft sediments brought to the surface by artesian discharge. The mudboils discharge fine-grained sediments into Onondaga Creek, primarily in the form of clay minerals. The history of mudboil loading to Onondaga Creek is poorly known, thus the total amount of sediment deposited in the creek in unknown. Kappel and McPherson (1998) reported the first documentation of mudboil occurrence in the area was in 1899 (local newspaper article). The sediment load from the mudboil depression area (MDA) to the creek in 1992 was about 30 ton/d. Major reductions of more than 90 % were subsequently achieved from an array of remedial actions (Kappel and McPherson) . Severe deterioration of water quality has been documented from downstream of the mudboils to the stream mouth following runoff events. Most of the sediment load delivered by these events was reported to be from resuspended stream sediment and eroded bank material located along the main channel of Onondaga Creek. Substantial modification of aquatic habitat was reported downstream of the mudboils relative to upstream conditions, including lower diversity, richness, and density. Despite its water quality problems, there is interest in Onondaga Creek for recreational purposes. There is research underway to improve the status of Onondaga Creek, including CSO diversion into engineered wetlands for additional treatment and the rehabilitation of riparian areas. If improved, Onondaga Creek could become an important resource to the community. Additionally, improving the quality of the creek would have positive impacts on Onondaga Lake.