To limit the spread of the COVID-19 virus conditions of lockdown were enforced by countries globally. Universities and schools revised the mode of delivery from contact teaching to online teaching and learning. This qualitative research was conducted at one university in South Africa and explored STEM discipline lecturers' reflections on the use of online technologies and the factors which enable or constrain online teaching and learning. Three lecturers from STEM disciplines involved in online teaching were purposively selected to participate in this study. Data were generated via semi-structured interviews and reflective journals. The findings reveal that lecturers supplement the use of Moodle and Zoom with WhatsApp, the factor that enabled online teaching was the availability of data to lecturers and students. In contrast, the factors that constrained online teaching and learning were the technical training received for online teaching, the mismatch between pedagogy and students' learning styles, the pressure of balancing work-home life and assumptions made about the availability of conducive home environments for learning, connectivity, and availability of devices for online learning. These findings have implications for professional development for online teaching and recommend that universities adopt WhatsApp to be a formal platform for online teaching and learning.