According to the Handbook of Psychology (Weiner, Freedheim), midstream approaches are those which are used with populations who are at risk, or in danger of becoming at risk, of depression.
When we speak of depression, we agree that this is a condition born out of both nature and nurture. While there is evidence that individuals can have a natural disposition for depression, others fall within the spectrum of a depressive episode as a result of environmental input. For example, illness, financial issues, grief and mourning, bad upbringing, anxiety and stress trigger depression symptoms, whether the individual has a propensity for it or not.
Back to the handbook, Weiner and Freedheim define midstream as
Interventions targeted toward defined populations for the purpose of reducing [..] behaviors typically in natural environments.
This means that a midstream approach will try to curb or change the natural environment where depression is likely to occur, become worse, or become epidemic, and control it from within.
An example of a midstream approach to depression is the current trend to offer routine counseling lessons at the middle school and high school levels in public schools. This intervention, as the definition offers, is meant to prevent the onset or spread of depression (and teenage suicide) by offering a viable route of ongoing communication in the natural environment of the students: right at the school.
This is how it works:
Given that teenagers and pre-adolescents have great biological changes occurring in their lives, their emotional and psychological issues exacerbate as their frontal lobes are still not fully developed. At school, all issues become worse with so much social stimuli, both good and bad, also attempting to shape the behaviors and emotions of children.
This causes the many behavioral and mental conflicts we see in adolescents when they get difficult or too emotional. Hormonal fluctuations, the awkwardness of growing up, and the social hierarchies that all teens use to differentiate themselves bring even more issues to the table and cause these young individuals to grow overstressed, depressed or irrational in many cases.
When the intervention is done midstream, it means that the counselor will educate the teens in terms of what exactly is happening inside their bodies that may lead them to feel down or depressed. Learning what causes the problem is an important part of the intervention because they also learn how to overcome those factors and deflect the issues that are caused by things that they really cannot keep from happening.
Therefore, these lessons help students understand themselves, realize what they are doing behavior-wise, find new ways to cope with depression (or avoid it altogether), and they also get to differentiate from real issues versus issues created by a depressive spectrum.