2026 ICD-10-CM Diagnosis Code Z77.121Contact with and (suspected) exposure to harmful algae and algae toxins

ICD-10-CM Codes›Z00–Z99›Z77-Z99›suspected

ICD-10-CM Z77.121
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Z77.121 is a billable ICD-10-CM diagnosis code for contact with and (suspected) exposure to harmful algae and algae toxins. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. Coders also document this condition as dermatosis caused by algae. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified status.

Code Identity

ICD-10-CM Code
Z77.121
Billable Status
Yes — Valid for Submission
Code Describes
Contact with and (suspected) exposure to harmful algae and algae toxins
Short Description
Contact w and exposure to harmful algae and algae toxins
Parent Code
Z77.12
Contact with and (suspected) exposure to hazards in the physical environment

Code Classification

ChapterZ00–Z99Factors influencing health status and contact with health services
SectionZ77-Z99Persons with potential health hazards related to family and personal history and certain conditions influencing health status
CategorysuspectedOther contact with and exposures hazardous to health (Z77)
This CodeZ77.121Contact with and (suspected) exposure to harmful algae and algae toxins

Code EditsBilling

Medicare Code Editor checks that affect claim validity for Z77.121.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Present on Admission (POA)Billing

Z77.121 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Dermatosis caused by algae
  • Exposure to algae bloom
  • Harmful algal bloom

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Contact with and (suspected) exposure to (harmful) algae bloom NOS
  • Contact with and (suspected) exposure to blue-green algae bloom
  • Contact with and (suspected) exposure to brown tide
  • Contact with and (suspected) exposure to cyanobacteria bloom
  • Contact with and (suspected) exposure to Florida red tide
  • Contact with and (suspected) exposure to pfiesteria piscicida
  • Contact with and (suspected) exposure to red tide

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Contact(with)
      • algae and algae toxins
    • Contact(with)
      • algae bloom
    • Contact(with)
      • blue-green algae bloom
    • Contact(with)
      • brown tide
    • Contact(with)
      • cyanobacteria bloom
    • Contact(with)
      • pfiesteria piscicida
    • Contact(with)
      • red tide (Florida)
    • Exposure(to)
      • algae and algae toxins
    • Exposure(to)
      • algae bloom
    • Exposure(to)
      • blue-green algae bloom
    • Exposure(to)
      • brown tide
    • Exposure(to)
      • cyanobacteria bloom
    • Exposure(to)
      • pfiesteria piscicida
    • Exposure(to)
      • red tide (Florida)

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR FAC025
Other specified status
Default principal diagnosis: inpatient No · outpatient Yes

Clinical InformationClinical

  • Harmful Algal Bloom

    an algal bloom where the algae produce powerful toxins that can kill fish, birds, and mammals, and ultimately cause illness in humans. the harmful bloom can also cause oxygen depletion in the water due to the death and decomposition of non-toxic algae species.

Patient EducationClinical

Water Pollution

We all need clean water. People need it to grow crops and to operate factories, and for drinking and recreation. Fish and wildlife depend on it to survive.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert Z77.121 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
V87.32 Contact/exp algae bloom
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Z77.121Overview

Is Z77.121 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report contact with and (suspected) exposure to harmful algae and algae toxins on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can Z77.121 be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because contact with and (suspected) exposure to harmful algae and algae toxins describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

Is Z77.121 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for contact with and (suspected) exposure to harmful algae and algae toxins on inpatient claims.

What is the ICD-9 equivalent of Z77.121?

Under the General Equivalence Mappings, contact with and (suspected) exposure to harmful algae and algae toxins converts to ICD-9-CM V87.32 (contact/exp algae bloom). The mapping is approximate, so confirm the match fits the documentation.