Cyanotoxins is an intracellular toxic substance that can be produced by a wide variety of planktonic cyanobacteria. Most commonly, it occurs in a genera of Microcystis, Dolichospermum (previously Anabaena), and Planktothrix. Cyanotoxins are released from the intracellular components of the cyanobacterial cells (algal bloom) into the surrounding water mostly during cell lysis (i.e., cell rupture). However, some cyanobacterial species are capable of releasing toxins (extracellular) into the water without cell rupture or death. Cyanobacteria were present on the earth 3.5 billion years ago since it has been colonized almost all terrestrial and aquatic ecosystems. They produce a high number of bioactive molecules, among which some of them are cyanotoxins. Excessive growth of algae in on freshwater ecosystem to form algal blooms in an anthropogenic activities and climatic changes might be arising a major problem of human and animal health. These cyanotoxins include cyclic peptides and alkaloids. Among the cyclic peptides the microcystins and the nodularins and alkaloids contain anatoxin-a, anatoxin-a(S), cylindrospermopsin, saxitoxins (STXs), aplysiatoxins, and lyngbyatoxin. Cyanotoxins may cause adverse health effects from mild skin rash to serious illness (death). When people are exposed to the drinking water containing microcystin and cylindrospermopsin, they could cause serious illness of liver and kidney damage. Acute illnesses like hay fever, skin rashes, respira-tory and gastrointestinal distress were also raised by short-term exposure of cyanotoxins in recreational activities. Cyanotoxins can be grouped according to their biological effects as hepatotoxins, neurotoxins, cytotoxins, and dermatotoxin. During water treatment cyanobacteria produce the algal toxins. Aplysiatoxin produced by Schizothrix, which comes under dermatotoxins. Lipopolysaccharide endotoxin is also produced by certain Cyanobacteria includ-ing Schizothrix calcicola. Climate change, as well as progressive eutrophication, is responsible for the global expansion and increased frequency of cyanobacterial blooms in aquatic environments. This chapter presents the knowledge that has evolved on the topic of toxins produced by Schizothrix. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023.