In DC, "crossing the river" means crossing the Anacostia River, which has been a significant divide between black and white communities in DC. The river isn't an absolute boundary, but when I was growing up in the area, I associated Anacostia and areas east of the river with danger - crime and violence and drugs and poverty. East of the Anacostia River, the demographics are majority black, with significant low-income areas. As a white boy, there weren't many reasons for me to ever go there.
I crossed the river last weekend, like I've been doing for over ten years now, to participate in a Sierra Club program called Inner City Outings, with the mission of providing nature experiences for urban youth. We've been doing monthly outings with this particular low-income housing community in Anacostia for over twenty years - I don't know the history of how we started with this community, but we're taking out kids whose parents came out with us, twenty years ago...
I once asked one of the participant youth what he'd think if I moved into his neighborhood, and he said, "For real? I'd think you was a crackhead". There aren't many good reasons for white people to be in this neighborhood. It's pretty calm now, but this still isn't an area where I'd feel safe walking at night, if I didn't know the community, and even as is, I stay alert. It's hard for me to imagine what it was like during the bad years. When we walk the neighborhood on Saturday mornings, we often find empty liquor bottles and discarded drug baggies and condoms, and sometimes teens and young men hanging out smoking weed. There's less of that now that there used to be, but it's still a good indicator of what kind of fun people where having the night before. We've seen shrines of plastic flowers and plush toys fade and moulder, and "R.I.P" tags on the walls, tributes to friends, relatives and neighbors who died violently.