Document And Entity Information - USD ($)	12 Months Ended
	Mar. 31, 2020	Jun. 16, 2020	Sep. 30, 2019
Document Information [Line Items]
Entity Registrant Name	Cyanotech Corp
Entity Central Index Key	0000768408
Trading Symbol	cyan
Current Fiscal Year End Date	--03-31
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding (in shares)		6,028,312
Entity Public Float			$ 7,852,346
Entity Shell Company	false
Document Type	10-K
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Title of 12(b) Security	Common Stock, $0.02 par value per share