Almost certainly it is a filament of Spirogyra sp.
Cell at center outlined. Thick black line indicates chloroplast. Dotted black line is portion of chloroplasts shielded (hidden) by some other portion of chloroplasts. Chloroplasts are helical (spring-like). Some of the pyrenoids (nearmost to eye, not shielded) marked with blue ring. Other pyrenoids not shown to avoid complication. The grey bubble-like thing outlined and dotted with red, may be the nucleus (nucleus is usually difficult to see when not stained). Cell wall marked with brown. Septum between 2 successive cells, seems to be plain septum.
Number of chloroplast in Spirogyra depends upon species. The number can range from 1 to 15* or 16. In the cell at center, There are 4 chloroplast being seen.
Algae /B.R. Vashista, A.K. Sinha, V.P. Singh/ S. Chand Publication / 2-colour revised edition.