The invention provides a method of monitoring influx of a fluid to a hydrocarbon producing well comprising providing at least one tracer release apparatus in a hydrocarbon producing well at an influx location. The at least one tracer release apparatus comprises a fluid volume and a tracer material located in the fluid volume. The method comprises shutting in the tracer release apparatus during production to increase the concentration of tracer molecules in the fluid volume; releasing the tracer molecules from the tracer release apparatus into the production flow and detecting the presence of tracer downstream of the influx location.