We used a sequential synthesis problem to investigate novice teachers' conceptual difficulties in hydrodynamics. Twenty-one new secondary level physics teachers from various regions of China, who had been in service for no more than 2 years, participated in the study. Each participant completed a written hydrodynamics problem consisting of four questions, all of which were related to a situation about water flowing in a long, nonuniform tube of different cross sections, heights, and orientations. Analysis of the teachers' written performances exposed a number of errors. To further investigate their underlying notions about hydrodynamics, we conducted one-on-one interviews with 13 teachers selected randomly from those making such errors on the written test. The interviews revealed three major categories of errors about hydrodynamics held by our novice teachers. These relate to (a) ontological confusions and misuse of properties associated with solid, liquid, and gas; (b) deficient perceptions of force-motion and work-energy analysis; and (c) mischaracterizations about the nature of Bernoulli's equation and the quantities therein. Here, we not only replicated some of the literature-reported misconceptions but also uncovered new ontological notions of hydrodynamics held by physics teachers, an underresearched population on this topic.