The Algae Estimator app allows anyone to enter simple measurements to determine the likelihood for an algal bloom or harmful algal bloom (toxic HAB from Cyanobacteria) occurring in shallow lake waters. The user can enter direct values for algae concentrations for either total or cyanobacterial Chlorophyll a values, or - if those are not available - from the easy to measure Secci Depth and dissolved Oxygen data as well as Temperature and Phosphate values of the lake. Hints on how these measurements can be done in an easy manner are provided within the App. A weather forecast option and GPS data for measurement sites are provided as well. Data can be stored and reviewed in the app for later use and evaluation. The app uses the user-entered measurements to predict whether or not there will be an algae bloom in the body of water and if so, how many hours it will be until the algae reaches a harmful level. Harmful algae blooms can cause bodies of water to be unusable for recreation and drinking, so predicting harmful algae blooms is useful in order to take precautionary measures.