Rainbow River Algae and Sediment Assessment Project

This project will help develop techniques to control algae and restore aquatic plants in the lower portion of the Rainbow River.


In the lower portions of the Rainbow River, native aquatic vegetation may be decreasing while various types of algae, such as filamentous macroalgae (Lyngbya) and phytoplankton, may be increasing. An increase in algae downstream is typical in most rivers as the river’s velocity — the speed at which water flows — decreases and water residence times increase. However, large amounts of algae growth can cause reduced water clarity and extreme fluctuations in dissolved oxygen, which is stressful to aquatic life. 

The Rainbow River and its immediate surroundings also were mined for phosphate in the early part of the twentieth century, and there is concern these former mines release nutrients into the river that may be increasing the presence of algae.

Project Overview 

This project investigated the relationships between water chemistry, river sediments and aquatic plants. The focus was on the middle and lower portions of the river where aquatic plant communities may be changing. Sediments in the river were examined to determine if they are a nutrient source contributing to increased algae in the lower river. The project also looked at the feasibility of modifying sediments in the river to reduce the abundance of algae and restore desirable aquatic plants such as strap-leaf Sagittaria. 

Another phase of the project will examine the impact of former phosphate mines on the lower river. If they are discovered to be a source of nutrients or algae, a feasibility study will be done on potential remediation projects. 

Project Partners

The District worked with the University of Florida on this project.


The project started in the summer of 2014 and was completed in 2017. An additional investigation into whether there is a correlation between iron concentrations and filamentous algae growth in Rainbow River began in 2021 and was completed in 2022.