Task: Question Answering
Input (English): Passage: The Ocklawaha River flows north and joins the St. Johns as the largest tributary, and one of significant historical importance. The Ocklawaha (also printed as Oklawaha) drainage basin expands through Orange, Lake, Marion, and Alachua Counties, comprising a total of 2,769 square miles (7,170 km2). Ocala, Gainesville, and the northern suburbs of the Orlando metropolitan area are included in this basin. There are two headwaters for the Ocklawaha: a chain of lakes, the largest of which is Lake Apopka in Lake County, and the Green Swamp near Haines City in Polk County, drained by the Palatlakaha River. The Silver River, fed by one of Florida's most productive springs expelling 54,000,000 US gallons (200,000,000 L) daily, is located about midway along the 96-mile (154 km) Ocklawaha.Confederate Captain John William Pearson named his militia after the Ocklawaha River called the Ocklawaha Rangers in the American Civil War. Prior to the civil war, Pearson ran a successful health resort in Orange Springs. After the civil war Pearson's Orange Springs resort declined in popularity due to the increasing attention to nearby Silver Springs—the source of the Silver River—at the turn of the 20th century, popularizing the Ocklawaha. Georgia-born poet Sidney Lanier called it "the sweetest waterlane in the world" in a travel guide he published in 1876. The river gave Marjorie Kinnan Rawlings access to the St. Johns from her homestead at Orange Lake. The region served as a major fishing attraction until a decline in water quality occurred in the 1940s, and since then further degradation of the river and its sources have occurred. In particular, Lake Apopka earned the designation of Florida's most polluted lake following a chemical spill in 1980 that dumped DDE in it.  It has experienced chronic algal blooms caused by citrus farm fertilizer and wastewater runoff from nearby farms.The proliferation of largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus), and bluegill (Lepomis macrochirus) in central Florida is a major attraction for fishermen from all over the country. The St. Johns is home to 183 species of fish, 55 of which appear in the main stem of the river. One, the southern tessellated darter (Etheostoma olmstedi) is found only in the Ocklawaha. Some are marine species that either migrate upriver to spawn or have found spring-fed habitats that are high in salinity, such as a colony of Atlantic stingrays (Dasyatis sabina) that live in Lake Washington in the upper basin. Ocean worms, snails, and white-fingered mud crabs (Rhithropanopeus harrisii) have also been found far upriver where tidal influences are rare. In contrast, American eels (Anguilla rostrata) live in the St. Johns and Ocklawaha and spawn in the Sargasso Sea in the middle of the Atlantic Ocean. After a year living in the ocean, many of them find their way back to the St. Johns to live, then, prompted by the phases of the moon, make the return journey to spawn and die. 
Question: What two waterways join as the largest tributary?
Output (English): St. Johns.