REUs or Research Experiences for Undergraduates are NSF funded summer programs that give undergrads full-time research experience. It is especially helpful to students at institutions that do not have a graduate school.
In 2017 I participated in an REU program for community college students at the Center for Dark Energy Biosphere Investigations at the University of Southern California, where I worked to characterize a novel marine bacterial isolate.
In 2018 my REU work focused on agricultural nitrogen pollution as part of the Center for Climate and Aerosol Research at Portland State University.