 The historic Islais Creek , the largest body of water in the city covering an area of nearly 5 @,@ 000 acres ( 7 @.@ <unk> sq mi ; 20 @.@ 234 km2 ) , had two main branches . One originated near the southern slope of Twin <unk> , slightly north of <unk> Drive . It flowed downstream southeastward through the Glen Canyon Park <unk> Bosworth Street and eventually reaching the bottom of the Mission Street viaduct at I @-@ 280 . The other branch began at the intersection of Cayuga Avenue and Regent Street . It flowed generally eastward along Mission Street and reached the I @-@ 280 viaduct . Together , as a wider creek , it ran parallel to <unk> Boulevard and I @-@ 280 and emptied into the Islais Creek estuary , near Industrial Street and <unk> Avenue . <unk> Creek , a nearby creek that originated from <unk> Valley , also joined Islais Creek at the César <unk> Boulevard and Evans Avenue intersection . 
