The historic Tibbetts Brook flows from just north of New York City into the Bronx, where part of it has become the lake in Van Cortlandt Park (it was originally a millpond, before the city bought the land to turn into a park). Today it flows into the combined sewer system just south of the park.
The New York City Parks Department, as well as local groups, have made some suggestions for daylighting this stream so that the significant waterflow it represents will be taken out of NYC's overburdened sewer system. I think that this is both a great idea and also a very realistic idea, as the terrain-- the topography of the landscape, the amount of available land, etc-- make it quite possible to re-create the historic waterway aboveground once again. It will cost a lot of money, of course, but I expect that this is the first significant daylighting project that will be achieved within NYC.
Note - I made these info sheets originally just as a way to tell people about the old streams and the sewers that have replaced them in NYC. I thought it was funny, for information about old streams that no longer existed, to present it as a flyer for a tour that didn't actually exist either. It was only a few years later than I began to develop actual walking tours where I would take people above-ground along the old routes of these streams. We only walk above-ground, but we peer down a few manhole covers along the way so that we can actually see the water flowing below (which is nowadays a mixture of natural groundwater and combined sewage together).