Abstract: The present invention comprises compositions and methods for forming an endovascular occlusion to treat conditions such as aneurysms, arterio-venous malformations, excessive blood supply to tumors, massive vascular hemorrhaging, and other conditions which require an embolization to alleviate the condition. Embodiments of the present invention comprise compositions and methods that use calcium alginate, without or without endovascular coils or similar devices, to form occlusions at a site within the mammalian body targeted for occlusion.